Method and device for measuring surface potential distribution, method and device for measuring insulation resistance, electrostatic latent image measurement device, and charging device

ABSTRACT

A surface potential distribution measurement method and device including setting a sample having a surface with a surface potential distribution in a sample installation unit wherein both an electric field intensity formed on the sample surface and a potential bias component of the sample are variable, and scanning the sample surface in a one-dimensional or two-dimensional manner by irradiating a charged particle beam to the sample. The method also includes obtaining a detection signal from charged particles generated by the scanning, to measure the surface potential distribution of the sample by varying the electric field intensity and the potential bias component in order to control a quantity of the detection signal obtained from the charged particles.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application is a divisional of U.S. application Ser. No.12/143,318 filed Jun. 20, 2008 now U.S. Pat. No. 7,783,213, which is adivisional of U.S. application Ser. No. 11/751,671 filed May 22, 2007now U.S. Pat. No. 7,400,839 issued Jul. 15, 2008, which is a divisionalof U.S. application Ser. No. 11/001,048 filed Dec. 2, 2004 now U.S. Pat.No. 7,239,148 issued Jul. 3, 2007, and in turn claims priority to JP2003-406002 filed Dec. 4, 2003, JP 2004-031910 filed Feb. 9, 2004, JP2004-094245 filed Mar. 29, 2004 and JP 2004-272069 filed Sep. 17, 2004the entire contents of each of which are hereby incorporated herein byreference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a method and device for measuring asurface potential distribution, a method and device for measuring aninsulation resistance, an electrostatic latent image measurement device,and a charging device.

2. Description of the Related Art

FIG. 12 shows the composition of an electrophotographic image formingapparatus in which an electrostatic latent image is formed on thephotoconductor drum by the imaging process. To output an image by theelectrophotographic image forming apparatus, including the copiers andthe laser printers, the following imaging process is usually carriedout.

As shown in FIG. 12, the image forming apparatus comprises the chargingunit 101, the exposure unit 102, the development unit 103, the transferunit 104, the fixing unit 105, the cleaning unit 106, and the electricerasing unit 107 which are arranged around the photoconductor drum 108.And the imaging process which includes the following steps (1) to (7) isrepeated for every image formation:

(1) Charging: the photoconductor is charged uniformly.

(2) Exposure: light is irradiated to the photoconductor, the electriccharge is removed partially, and the electrostatic latent image isformed on the photoconductor.

(3) Development: the electrostatic latent image is converted into thevisible image by using the charged particles (toner).

(4) Transferring: the visible image developed is transferred to paper orother recording material.

(5) Fixing: the transferred image is heated and is fixed to therecording material.

(6) Cleaning: the remaining toner on the photoconductor is cleaned.

(7) Electric Erasing: the residual charge on the photoconductor iseliminated.

Each process factor and process quality in each of the above steps ofthe imaging process affect the final output image quality greatly. Inrecent years, in addition to high image quality, the demands forincreasing the durability, the stabilization, and the energy saving, aremade, and it is necessary to raise the process quality of each of theabove imaging process steps.

In the imaging process, the electrostatic latent image formed on thephotoconductor by the exposure is the factor which directly affects theaction of the toner particles, and it is necessary to measure accuratelythe surface potential distribution on the photoconductor surface. Forthis reason, it is important to evaluate the quality of theelectrostatic latent image on the photoconductor. The process quality ofeach of the imaging process steps can be improved by measuring theelectrostatic latent image of the photoconductor and feeding back to thedesign.

The method of observing or measuring a surface potential distribution onthe surface of an object by the scanning of electron beam is known (forexample, Japanese Laid-Open Patent Application No. 03-049143).

In this method, the electron beam is scanned on the measurement samplehaving a surface potential distribution, and the secondary electrongenerated on the measurement sample associated with the scanning of theelectron beam is detected so that the surface potential distribution isobserved or measured. The measurement sample used as a candidate formeasurement must be, for example, an LSI chip which is capable ofretaining electric charge on its surface for a sufficiently long time.

The electrostatic latent image which is formed on the photoconductordrum in the analog or digital electrophotographic copiers or laserprinters by the charging and exposure is a factor which directly affectsthe action of the toner particles, and, for this reason, the qualityevaluation of the electrostatic latent image on the photoconductor isimportant.

If the electrostatic latent image on the photoconductor is measured andthe result of measurement can be fed back to the design of the copiersor the printers, then it is possible to attain improvement in processquality in the charging process or the exposure process. Consequently,the further improvement in the quality of image, the durability andstability, or the energy saving can be expected.

However, the electrostatic latent image formed on the photoconductor maydisappear for a short time (about dozens seconds) due to the darkdecaying of the photoconductor, and there is little time which can beused for the measurement. If the method of Japanese Laid-Open PatentApplication No. 03-049143 is used to measure the surface potentialdistribution, the electrostatic latent image on the photoconductor willdisappear in the preparation stage of the measurement, and practicallythe measurement cannot be performed.

Furthermore, there is proposed the technique of measuring theelectrostatic latent image on the photoconductor having the darkdecaying (for example, see Japanese Patent Applications No. 2003-295696and No. 2004-251800 which are assigned to the assignee of the presentinvention).

The well-known method of measuring the surface potential distributionuses the sensor head, such as the cantilever, which is brought close tothe sample having the surface potential distribution, and theelectrostatic attraction and induced current produced at that time asthe interaction are measured, and the measured current is converted intothe potential distribution. For example, the electrostatic-attractiontype is marketed as the SPM (Scanning Probe Microscope). And there aresome known techniques of the induced current type (for example, JapanesePatent No. 3009179 and Japanese Laid-Open Patent Application No.11-184188).

However, in order to use the known method, it is necessary to bring thesensor head close to the sample. In order to obtain the 10-micrometerspatial resolution in this case, it is necessary to set the distancebetween the sensor and the sample to 10 micrometers or less.

When taking into consideration the proximity conditions, there are thefollowing problems. Although the method can be uses for otherapplications, it cannot practically be used for the measurement of theelectrostatic latent image. Namely, the distance measurement is neededabsolutely, the measurement takes time and the latent-image statechanges during the measurement, the electric discharge and adsorptiontake place, and the sensor itself disturbs the electric field.

For this reason, the method of visualizing the electrostatic latentimage is usually taken as the practical measurement method. That is, theelectric charge is given to the toner in the form of colored powder-likeparticles, the development is performed by the Coulomb force which worksbetween the charged toner and the electrostatic latent image, and thesurface potential distribution of the electrostatic latent image ismeasured by transferring this toner image to the paper or the recordingtape.

However, according to the above method, there is the problem that itdoes not mean the measurement of the surface potential distribution ofthe electrostatic latent image itself since the measurement is performedafter the processes of development and transferring are performed,

As mentioned above, practically the electrostatic latent image cannot bemeasured by the method of irradiating the electron beam to the samplewhich is capable of retaining electric charge on its surface (the LSIchip), and the method of bringing the sensor head, such as thecantilever, close to the sample, and measuring the electrostaticattraction and the induced current.

To overcome the above problem, there is proposed the technique ofmeasuring the electrostatic latent-image distribution in which thecharged particle beam or electron is irradiated, in advance, to thesample (for example, Japanese Laid-Open Patent Applications No.2003-295696 and No. 2003-305881 which are assigned to the assignee ofthe present invention). In addition, the electrostatic latent imagemeans the image in the state where the electric charge is distributedover the dielectric substance.

Namely, in the proposed technique, if the potential distribution occurson the surface of the sample when the electron is irradiated, theelectric field distribution according to the surface potentialdistribution is formed in space. For this reason, the secondary electrongenerated by the incident electron is put back by the electric field,and the quantity of the secondary electron which reaches the detector isdecreased.

By using the above-described feature, the portion with the high fieldintensity becomes dark and the portion with the low field intensitybecomes bright so that the contrast is formed, and the contrast imageaccording to the surface potential distribution can be detected.Therefore, the exposed portion becomes black and the non-exposed portionbecomes white after the exposure, so that the thus formed electrostaticlatent image can be measured.

FIG. 13 shows the relation between the measured electric field intensityobtained by detecting the secondary electron generated by the incidentelectron and the light-and-dark image produced according to the surfacepotential distribution.

It is possible to measure the electrostatic latent image by using theabove method. However, as shown in FIG. 13, even if the electric fieldintensity is high, the contrast image will not necessarily become theluminance signal proportional to the electric field intensity, and thecontrast image is likely to become the light-and-darkness image with thetendency of the binary signal.

In addition, it is assumed that, concerning the electric field intensitydescribed, the sign of the electric field vector on the side of theincidence electron in the direction perpendicular to the sample surfaceis positive.

As for the contrast image of lightness and darkness, as illustrated, thethreshold level is in the vicinity of the level where the electric fieldintensity is zero. However, there is the electric field intensity (Eth)which is required for attachment of the charged particles (toner) in theactual electrophotographic printing process, and it is important tomeasure the diameter of the latent image at the level of Eth.

If the electric field intensity distribution can be approximated with asmooth curve like the Gaussian distribution, it is possible to computethe diameter of the latent image at the Eth level. However, the errorcomponents may be contained in the actual case, and it does not usuallybecome the smooth curve like the Gaussian distribution. Acquiringdirectly the image as the contrast image at the Eth level is necessaryfor the practical case.

Moreover, FIG. 14 shows the image acquisition method (Japanese Laid-OpenPatent Application No. 03-049143) in which the back bias voltage isapplied in the composition of the sample and the electrode. In thisimage acquisition method, the voltage of the back bias is applied to theback surface of the sample 32 in order to obtain a proper potentialdistribution, and the electrostatic latent image according to theapplied electron beam is acquired.

However, in this method, the electric field intensity on the frontsurface of the sample is not affected even when the voltage of the backbias is applied to the back surface of the sample 32. The effect thatthe threshold level of the potential distribution is changed cannot beproduced. In addition, in the composition of FIG. 14, the referencenumeral 33 denotes the conductor, 34 denotes the secondary electrondetector, 35 denotes the power supply, and 37 denotes the objectivelens, respectively.

SUMMARY OF THE INVENTION

An object of the present invention is to provide an improved surfacepotential distribution measuring technique in which the above-describedproblems are eliminated.

Another object of the present invention is to provide a surfacepotential distribution measurement method and device which can measurethe surface potential distribution of an object with high precisionwithout being influenced by the secondary electron.

Another object of the present invention is to provide a surfacepotential distribution measurement method and device which can measurethe surface potential distribution of the electrostatic latent imageformed on the photoconductor having the dark decaying with highprecision.

Another object of the present invention is to provide a surfacepotential distribution measurement method and device which can measurethe surface potential distribution on the surface of the dielectricsubstance with high resolution in the order of micrometers.

Another object of the present invention is to provide a surfacepotential distribution measurement method and device which can measurethe electrostatic latent image on the surface of the photoconductor withhigh precision in the order of micrometers.

Another object of the present invention is to provide an insulationresistance measurement method and device which can measure theinsulation resistance of a sample, such as a photoconductor, with highprecision in the order of micrometers.

Another object of the present invention is to provide a charging devicewhich efficiently charges the sample surface to the desired potentialwith high precision.

Another object of the present invention is to provide an electrostaticlatent image measurement device which efficiently charges the surface ofa latent-image support object to the desired potential with highprecision.

The above-mentioned objects of the present invention are achieved by amethod of measuring a surface potential distribution, the methodcomprising the steps of: scanning a sample having a surface with asurface potential distribution using a charged particle beam in atwo-dimensional manner; obtaining a detection signal caused by thetwo-dimensional scanning, to measure the surface potential distribution;and detecting charged particles, other than charged particles of thecharged particle beam incident to the sample surface by thetwo-dimensional scanning, with which components of an incidence velocityvector of the charged particles in a direction perpendicular to thesample surface are reversed, so that a detection signal indicating anintensity according to the detected charged particles is obtained incorrespondence with a position on the sample surface.

The above-mentioned objects of the present invention are achieved by adevice for measuring a surface potential distribution, the devicecomprising: a charged particle beam scanning unit scanning a samplehaving a surface with a surface potential distribution using a chargedparticle beam in a two-dimensional manner; a capture unit capturingcharged particles, other than charged particles of the charged particlebeam incident to the sample surface by the two-dimensional scanning,with which components of an incidence velocity vector of the chargedparticles in a direction perpendicular to the sample surface arereversed; and a measurement unit obtaining a detection signal indicatingan intensity according to the captured charged particles incorrespondence with a position on the sample surface, so that thesurface potential distribution is measured with the detection signal.

According to the preferred embodiment of the present invention, thecharged particle detected is the charged particle which constitutes thecharged particle beam which scans the sample surface, and is not thesecondary electron generated on the sample surface. Since the secondaryelectron does not arise, it is possible to measure the surface potentialdistribution easily and accurately. Moreover, the measurementappropriate for the electrostatic latent image formed on thephotoconductor sample can be performed.

The above-mentioned objects of the present invention are achieved by amethod of measuring a surface potential distribution, the methodcomprising the steps of: setting a sample having a surface with asurface potential distribution in a sample installation unit whereinboth an electric field intensity formed on the sample surface and apotential bias component of the sample are variable; scanning the samplesurface in a one-dimensional or two-dimensional manner by irradiating acharged particle beam to the sample; and obtaining a detection signalfrom secondary charged particles generated by the scanning, to measurethe surface potential distribution of the sample, wherein themeasurement is performed by varying the electric field intensity and thepotential bias component in order to control a quantity of the detectionsignal obtained from the secondary charged particles.

The above-mentioned objects of the present invention are achieved by amethod of measuring a surface potential distribution, the methodcomprising the steps of: setting a sample having a surface with asurface potential distribution in a sample installation unit whereinboth an electric field intensity formed on the sample surface and apotential bias component of the sample are variable; scanning the samplesurface in a one-dimensional or two-dimensional manner by irradiating acharged particle beam to the sample; obtaining a detection signal fromsecondary charged particles generated by the scanning, to measure thesurface potential distribution of the sample, wherein the measurement isperformed repeatedly by varying the electric field intensity and thepotential bias component at a plurality of times in order to control aquantity of the detection signal obtained from the secondary chargedparticles, so that a profile of the surface potential distribution iscomputed based on a plurality of measurement results thus obtained.

The above-mentioned objects of the present invention are achieved by adevice for measuring a surface potential distribution in which a samplehaving a surface with a surface potential distribution is set in asample installation unit, wherein both an electric field intensityformed on the sample surface and a potential bias component of thesample are variable, the device comprising: a charged particle beamscanning unit scanning the sample surface in a one-dimensional ortwo-dimensional manner by irradiating a charged particle beam to thesample; a detector capturing secondary charged particles generated inconformity with the surface potential distribution of the sample by thescanning; a measurement unit obtaining a detection signal, indicating anintensity according to the captured secondary charged particles, incorrespondence with a position on the sample surface, to measure thesurface potential distribution of the sample; an electric fieldintensity control unit varying the electric field intensity in order tocontrol a quantity of the detection signal obtained; and a potentialbias control unit varying the potential bias component in order tocontrol a quantity of the detection signal obtained.

The above-mentioned objects of the present invention are achieved by adevice for measuring an electrostatic latent image distribution of aphotoconductor, the device comprising: a charging unit creating anelectric charge on a surface of a photoconductor sample by irradiatingan electron beam to the photoconductor sample; an optical-system unitscanning the surface of the sample by irradiating light to the sample sothat an electrostatic latent image is formed on the sample surface; asample installation unit in which the sample is set, wherein both anelectric field intensity formed on the sample surface and a potentialbias component of the sample are variable; a detector capturingsecondary charged particles generated in conformity with anelectrostatic latent-image distribution of the sample by the scanning; ameasurement unit obtaining a detection signal, indicating an intensityaccording to the captured secondary charged particles, in correspondencewith a position on the sample surface, to measure the electrostaticlatent-image distribution of the sample; an electric field intensitycontrol unit varying the electric field intensity in order to control aquantity of the detection signal obtained; and a potential bias controlunit varying the potential bias component in order to control thequantity of the detection signal obtained.

According to the preferred embodiment of the present invention, thesurface potential distribution in the vertical direction of thedielectric-substance sample can be measured with high resolution in theorder of micrometers.

The above-mentioned objects of the present invention are achieved by aninsulation resistance measuring method comprising the steps of: charginga surface of a sample to give an electric field intensity in a thicknessdirection of the sample; scanning the charged surface of the sample in atwo-dimensional manner by irradiating a charged particle beam to thesample; obtaining a detection signal generated by the scanning; andmeasuring a dielectric intensity of the sample based on the detectionsignal obtained.

The above-mentioned objects of the present invention are achieved by aninsulation resistance measurement device comprising: a support unitholding a sample whose dielectric intensity is to be measured; acharging unit charging a surface of the sample held by the support unitand giving an electric field intensity in a thickness direction of thesample; a scanning unit scanning the charged surface of the sample in atwo-dimensional manner by irradiating a charged particle beam to thesample; a signal-detection unit obtaining a detection signal generatedby the scanning of the scanning unit; and a measurement unit measuringthe dielectric intensity of the sample based on the detection signalobtained by the signal-detection unit.

The above-mentioned objects of the present invention are achieved by alatent-image support object having a dielectric intensity measured by aninsulation resistance measuring method, wherein the insulationresistance measuring method comprises the steps of: charging a surfaceof the latent-image support object to give an electric field intensityin a thickness direction of the latent-image support object; scanningthe charged surface of the latent-image support object in atwo-dimensional manner by irradiating a charged particle beam to thelatent-image support object; obtaining a detection signal generated bythe scanning; and measuring the dielectric intensity of the latent-imagesupport object based on the detection signal obtained, wherein thelatent-image support object has a percentage of an insulation resistanceregion which is 99% or more when the electric field intensity given inthe thickness direction of the latent-image support object is above 30V/micrometer and below 40 V/micrometer and an amount of electric chargeirradiated to the latent-image support object is above 1E-8 coulomb/mm².

According to the preferred embodiment of the present invention, it ispossible to measure the insulation resistance of the photoconductor,with high precision in the order of micrometers.

The above-mentioned objects of the present invention are achieved by acharging device which creates electric charge on a beam-irradiation-sidesurface of a sample by irradiating a negative charged particle beam,including electrons or negative charged ions, to the sample, wherein thecharging device is provided to meet the conditions E1>E0−Vg, E0>0, andE1>0 where E0 is an acceleration voltage of electrons at which asecondary-electron-emission ratio of the same is equal to 1 when a backsurface of the sample opposite to the beam-irradiation-side surface isgrounded, E1 is an acceleration voltage for accelerating negativecharged particles of the beam, and Vg is a back potential applied to theback surface, so that a desired negative charging potential is formed onthe sample.

The above-mentioned objects of the present invention are achieved by anelectrostatic latent-image measurement device comprising: a chargingdevice creating electric charge on a beam-irradiation-side surface of asample by irradiating a negative charged particle beam, includingelectrons or negative charged ions, to the sample; and an exposureoptical system irradiating light to the charged surface of the sample sothat an electrostatic latent image according to an electric chargedistribution of the sample surface is formed, wherein the chargingdevice is provided to meet the conditions E1>E0−Vg, E0>0 and E1>0 whereE0 is an acceleration voltage of electrons at which asecondary-electron-emission ratio of the same is equal to 1 when a backsurface of the sample opposite to the beam-irradiation-side surface isgrounded, E1 is an acceleration voltage for accelerating negativecharged particles of the beam, and Vg is a back potential applied to theback surface, so that a desired negative charging potential is formed onthe sample.

According to the preferred embodiment of the present invention, it ispossible to efficiently charge the sample surface to the desiredpotential with high precision by setting up the back potential Vgappropriately.

BRIEF DESCRIPTION OF THE DRAWINGS

Other objects, features and advantages of the present invention will beapparent from the following detailed description when reading inconjunction with the accompanying drawings.

FIG. 1A and FIG. 1B are diagrams showing the composition of the surfacepotential distribution measurement device in the preferred embodiment ofthe invention.

FIG. 2A and FIG. 2B are diagrams for explaining the principle ofmeasurement of surface potential distribution.

FIG. 3 is a diagram for explaining the measurement of surface potentialdistribution.

FIG. 4 is a diagram for explaining the application of uniform biaspotential to the surface potential distribution on the surface of thesample.

FIG. 5 is a diagram for explaining the embodiment in which the chargedparticle beam is incident to the scanning region of the sample havingthe surface potential distribution from the inclined direction to thevertical direction.

FIG. 6 is a flowchart for explaining the procedure of measuring thelatent-image profile.

FIG. 7 is a diagram showing the composition of the surface potentialdistribution measurement device in the preferred embodiment of theinvention which measures the electrostatic latent image formed on thephotoconductive sample.

FIG. 8 is a diagram for explaining the formation of the electrostaticlatent image on the photoconductive sample.

FIG. 9 is a diagram for explaining an example of the irradiation of theoptical image to the photoconductive sample surface in the surfacepotential distribution measurement device of FIG. 7.

FIG. 10 is a diagram for explaining another example of the irradiationof the optical image to the photoconductive sample surface.

FIG. 11 is a diagram showing the composition of the surface potentialdistribution measurement device in another preferred embodiment of theinvention which measures the electrostatic latent image formed on thephotoconductive sample.

FIG. 12 is a diagram showing the composition of an electrophotographicimage forming apparatus in which an electrostatic latent image is formedon the photoconductor drum by the imaging process.

FIG. 13 is a diagram for explaining the relation between the measuredelectric field intensity obtained by detecting the secondary electrongenerated by the incident electron and the light-and-dark image producedaccording to the surface potential distribution.

FIG. 14 is a diagram for explaining the method of applying the back biasvoltage in the conventional method.

FIG. 15 is a diagram showing the composition of the surface potentialdistribution measurement device in the preferred embodiment of theinvention in which the charged particle irradiation unit, the sampleinstallation unit, and the secondary electron detecting unit arearranged.

FIG. 16 is a diagram showing an example of the connection of the sampleand the electrode installed in the sample installation unit in thesurface potential distribution measurement device of the presentembodiment.

FIG. 17 is a diagram showing another example of the connection of thesample and the electrode installed in the sample installation unitthrough the insulator in the surface potential distribution measurementdevice of the present embodiment.

FIG. 18A, FIG. 18B and FIG. 18C are diagrams showing examples of thegrid mesh electrode which is arranged above the beam incidence sidesurface of the sample.

FIG. 19A and FIG. 19B are diagrams for explaining the difference in thecontrast image between the case where there is no field intensity biasand the case where there is the electric field bias Eb applied.

FIG. 20 is a flowchart for explaining the procedure which computes thelatent-image profile of the surface potential distribution based on theplurality of measurement results which are obtained by measuring thesurface potential distribution repeatedly every time the electric fieldintensity is varied.

FIG. 21 is an enlarged diagram showing the composition of the principalpart of the photoconductor.

FIG. 22 is a diagram showing the composition of the surface potentialdistribution measurement device in another preferred embodiment of theinvention which can carry out the charging, the exposure, and theelectrostatic latent-image measurement.

FIG. 23 is a diagram showing the composition of the respective controlunits used for the preferred embodiment of FIG. 22.

FIG. 24 is a diagram showing the composition of the surface potentialdistribution measurement device in the preferred embodiment of theinvention which enables the measurement of the cylindrical-form sample.

FIG. 25 is a diagram showing the composition of the exposure opticalsystem in which the scanning mechanism is provided in the optical systemof the charged particle irradiation unit (electron beam irradiationunit) according to the invention.

FIG. 26A, FIG. 26B and FIG. 26C are diagrams showing the insulationresistance measurement device in the preferred embodiment of theinvention.

FIG. 27A and FIG. 27B are diagrams for explaining the detection of thesecondary electron.

FIG. 28A, FIG. 28B and FIG. 28C are diagrams for explaining the leakageof the electric charge by the breakdown in the photoconductor offunction separation type.

FIG. 29A and FIG. 29B are diagrams showing examples of the measurementresult.

FIG. 30 is a diagram for explaining the insulation resistancemeasurement device in another preferred embodiment of the invention.

FIG. 31 is a flowchart for explaining the procedure of insulationresistance measurement.

FIG. 32 is a diagram showing the composition of the electrostatic latentimage measurement device in the preferred embodiment of the invention.

FIG. 33 is a diagram for explaining the relation between accelerationvoltage and charging.

FIG. 34 is a diagram for explaining the relation between the irradiationtime of the electron beam and the charging potential.

FIG. 35 is a diagram for explaining the relation between accelerationvoltage and charging potential.

FIG. 36 is a diagram showing the measurement result in the presentembodiment.

FIG. 37 is a diagram for explaining an example of the latent-imageformation and the measurement.

FIG. 38 is a diagram showing an example of the exposure optical system.

FIG. 39 is a diagram for explaining the embodiment which measures theelectrostatic latent image of the photoconductor of cylinder form.

FIG. 40 is a diagram showing another embodiment which measures theelectrostatic latent image of the photoconductor of cylinder form.

FIG. 41 is a diagram showing another embodiment which measures theelectrostatic latent image of the photoconductor of cylinder form.

FIG. 42 is a diagram showing another embodiment which measures theelectrostatic latent image of the photoconductor of cylinder form.

FIG. 43 is a diagram for explaining the charging unit.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

A description will now be given of the preferred embodiments of theinvention with reference to the accompanying drawings.

FIG. 1A shows the composition of the surface potential distributionmeasurement device in the preferred embodiment of the invention. Thesurface potential distribution measurement device is provided to measurethe surface potential distribution of the sample 0. The respectivecomponents of this device are accommodated in the sealed casing 27, andthe inside of the sealed casing 27 can be decompressed to thesubstantially vacuum state by using the suction unit 29.

When the sample 0 is the electrophotographic photoconductor(photoconductive sample), the electrostatic latent-image formation unitwhich will be described later is also arranged in the sealed casing 27.

In the example of FIG. 1A, it is assumed that a surface potentialdistribution is formed on the sample 0, and the inside of the sealedcasing 27 is decompressed.

In the present embodiment, the electron beam is used as a chargedparticle beam which scans the sample 0 in a two-dimensional manner.Namely, the electron beam is generated by the electron gun 10, and itpasses through the beam monitor 13. The electron beam further passes andis converged at the position of the aperture 17 and the beam blanker 18by the condenser lens 15, and it is deflected in a two-dimensionalmanner by the scanning lens 19 of the deflecting coil. The thusdeflected electron beam is converged at the surface of the sample 0 bythe objective lens 21.

The beam monitor 13 is provided to monitor the intensity of the electronbeam emitted by the electron gun 10. The aperture 17 is provided tocontrol the current density (the number of irradiation particles perunit time) of the electron beam irradiated to the sample 0. The beamblanker 18 is provided to switch on and off the irradiation of theelectron beam.

The respective parts which are arranged around the irradiation path ofthe electron beam between the electron gun 10 and the sample 0 areelectrically connected to the power supply which is not illustrated, andthese are controlled by the control unit, such as the computer which isnot illustrated.

With the above composition of the surface potential distributionmeasurement device, the electron beam which is deflected in atwo-dimensional manner by the scanning lens 19 scans the surface of thesample 0 in a two-dimensional manner.

In the example of FIG. 1A, the surface or near the surface of the sample0 having the surface potential distribution is charged to negativepolarity, and the sample 0 has the surface potential distributionaccording to the charged state.

As shown in FIG. 1A, the back surface of the sample 0 is supported bythe support part 23. The support part 23 is made of a conductiveplate-like material, and it is grounded. The surface potentialdistribution of the sample 0 forms the potential barrier which causes astrong restitution to act on each electron of the electron beam in theclose vicinity of the surface of the sample 0.

As shown in FIG. 1B, it is assumed that the direction of z is taken tobe perpendicular to the surface of the sample 0, the x axis and they-axis are taken to be parallel to the sample surface, and thecoordinates (x, y) are set on the surface of the sample 0. The directionof y is taken to be perpendicular to the surface of the drawing.

At this time, if the region S which is scanned by the electron beam in atwo-dimensional manner is represented by S (x, y) using the2-dimensional coordinates, the conditions: 0 mm≦x≦1 mm. 0 mm≦y≦1 mm areset. The surface potential distribution currently formed in this regionS (x y) is represented by V (x, y) (<0).

Assuming that T is the time between the start T0 and the end TF of the2-dimensional scanning of the sample 0 by the electron beam, thecondition T0≦T≦TF is set, and there is the one-to-one correspondencebetween the time: T the scanning is performed and each scanning positionof the scanning region: S (x y).

FIG. 1B is a diagram for explaining the situation in the vicinity of thesample surface. The size of the scanning region S of the sample 0 isvariable with the setting of the magnification of the scanning lens 19.For example, the size of the scanning region S may be varied from thelow magnification of about 5 mm by 5 mm to the high magnification ofabout 1 micrometer by 1 micrometer. The situation of the scanning regionS is observable with the arbitrary magnification.

The speed of the electron beam emitted by the electron gun 10 is set tov, and the components of the speed v in the directions x, y, z are setto vx, vy, vz, respectively. Strictly speaking, the speed components vx,vy, and vz of each electron in the electron beam vary in connection withthe scanning of the electron beam. However, in the size of the actualmeasurement device, the distance from the objective lens 21 to thesurface of the sample 0 is some hundreds millimeters, and the scanningregion of the sample 0 is the size of about 5 mm×5 mm. Under suchconditions, it is possible to consider vx=vy=0 and vz=v substantially.

At this time, the kinetic energy of each electron which hits the surfaceof the sample 0 in the electron beam scanned is represented by mv^(2/)2where m is the mass of the electron. It is equal to the product of theacceleration voltage Va of the accelerator provided in the electron gun10 and the electron charge e, and the equation: mv²/2=eVa is met.

The surface potential distribution V (x, y) currently formed in thescanning region S (x, y) of the sample 0 has the same polarity as theelectron and acts as the potential barrier to the electron. If thecondition: mv²/2=eVa>−eV(x, y) is met, then the electron of the electronbeam passes the potential barrier and arrives at the surface of thesample 0.

On the contrary, if the condition: mv²/2=eVa<−eV(x·y) is met, then theelectron of the electron beam is slowed down by the potential barrier,the speed:vz of the electron is set to 0, and the electron is pushedback in the direction of incidence by the surface potential of thesample 0. That is, the speed:vz of the electron pushed back in this way(which is the components of the incidence velocity vector of the chargedparticle beam in the direction perpendicular to the sample surface) isreversed from the direction at the time of incidence to the oppositedirection.

FIG. 2A and FIG. 2B are diagrams for explaining the above-mentionedsituations. FIG. 2A shows the case where the electronic speed vz isreversed from the direction at the time of incidence under thecondition: Va<−V (x, y). FIG. 2B shows the case where the electron ofthe electron beam passes the potential barrier and arrives at thesurface of the sample 0 under the condition: Va>−V (x, y).

In the above-described surface potential distribution measurementdevice, the electron (which is called the speed components reversalelectron) whose components vz of the incidence velocity vector in thedirection (the direction of z) perpendicular to the sample surface arereversed by the restitution of the surface potential distribution:V (xy) is captured by the detector 25 (FIG. 1B).

As shown in FIG. 1B, the drawing-in voltage of the reverse polarity(positive polarity) to the polarity of the electron is applied to thedetector 25 by the power supply EA, and the speed components reversalelectron is captured with this drawing-in voltage.

The captured speed components reversal electron is amplified by theelectron multiplier etc., and is converted into a detection signalaccording to the intensity (the number of the speed components reversalelectrons captured per unit time).

Since the speed components reversal electron captured by the detector 25is opposed by the surface potential distribution:V (x y) of the sample0, the intensity F (T) of the speed components reversal electroncaptured at time T has the correspondence relation with the surfacepotential distribution:V {x (T), y (T)} having the parameter of the timeT.

In the above-described example, the speed components reversal electroncaptured by the detector 25 satisfies the condition Va<−V(x, y), themeasurement result means that the surface potential distribution:V (x y)of the sample 0 is divided into two regions with the accelerationvoltage Va of the electron gun 10 being considered a threshold ofmeasurement.

Namely, among the scanning region S (x, y), the region where the speedcomponents reversal electron is captured is the region of the surfacepotential distribution under the condition: −V(x y)>Va, and the regionwhere the speed components reversal electron is not captured is theregion of the surface potential distribution under the condition: −V(xy)<Va.

Therefore, by sampling the detection signal outputted from the detector25 at a suitable interval, it can be determined whether −V (x y) forevery small region corresponding to the sampling is larger than thethreshold Va or not.

In the above-described embodiment, the case where the electron beam isused as the charged particle beam has been described. Alternatively, ifa liquid-metal ion gun which generates an ion beam is used instead ofthe electron gun 10 of the above embodiment, it is possible to performthe measurement in which the ion beam is used as the charged particlebeam.

In the case of the surface-potential distribution of the sample 0 underthe condition V(x, y)>0, what is necessary is just to use the ions orprotons of the positive polarity, such as gallium, as the chargedparticles of the charged particle beam.

Generally, when the maximum of the absolute value of the surfacepotential distribution V (x, y) is set to Max |V(x, y)|, the scanning ofthe charged particle beam is performed on the condition that theacceleration voltage Va is Max |V(x, y)|, and it can be determined wherethe measured surface potential V (x y) is larger than the threshold Vaof measurement.

In the surface potential distribution V (x, y) (negative polarity) ofFIG. 3, the potential distribution of the surface of the sample 0 whenthe back surface of the support part 23 which supports the sample 0 isgrounded is illustrated. The surface potential at the center of thepotential distribution (x=0) is about −520V, and the surface potentialbecomes large in the minus direction and is equal to about −830V in thecircumference region that is distant from the center 0.01 mm or more.

In FIG. 3, the region S600 of the surface-potential distribution underthe condition V(x y)>−600V as a result of the measurement which isperformed by setting the acceleration voltage Va to −600V, and theregion S750 of the surface-potential distribution under the conditionV(x y)>−750V as a result of the measurement which is performed bysetting the acceleration voltage Va to −750V are illustrated. In theseregions S600 and S750, there are very few electrons which are detectedby the detector 25.

If the measurement is performed repeatedly by varying the accelerationvoltage Va in a plurality of steps, the regions into which the surfacepotential distribution V (x y) is divided are obtained for everyacceleration voltage Va (or the threshold of measurement) for everymeasurement, the overall state of the surface potential distribution V(x y) can be determined based on the plurality of measurement results.It is a matter of course that, if the step in which the accelerationvoltage Va is varied is made fine and the number of repeatedmeasurements is increased, accurate measurement is attained.

In the above embodiment, the acceleration voltage Va of the acceleratorprovided in the electron gun 10 is varied, so that the threshold ofmeasurement (the voltage used to separate the charged particles whosespeed components of the charged particle beam in the directionperpendicular to the surface of the sample are reversed, from thecharged particles which are not reversed and are incident to the samplesurface) is varied.

Alternatively, it is possible to use another method of changing thethreshold of measurement according to the invention, and in thisalternative method a uniform bias potential is applied to the surfacepotential distribution on the surface of the sample.

FIG. 4 shows the application of uniform bias potential to the surfacepotential distribution on the surface of the sample in the preferredembodiment of the invention. In FIG. 4, the support part 23A whichsupports the back surface of the sample 0 has the three layer structuresin which the dielectric layer 23 b is inserted between the electricconduction layers 23 a and 23 c, and the electric conduction layer 23 cis grounded and the bias voltage from the variable direct current powersupply EB is applied to the electric conduction layer 23 a.

If the bias voltage is applied to the electric conduction layer 23 a,the surface potential distribution on the surface of the sample 0 ischanged to the state in which the uniform bias potential is superimposedto the surface potential distribution of the sample 0.

In the case where the electron beam is used as the charged particlebeam, the acceleration voltage Va of the electron beam is enlargedbeforehand and the polarity of the bias voltage applied to the electricconduction layer 23 a is set to the negative polarity, so that the biaspotential which repels the electrons that are incident as the electronbeam is formed.

If the potential which is superimposed by the application of the biasvoltage is set to VB (<0) and the actual surface potential distributionof the sample 0 is indicated by V (x, y), the electric field which actson the incidence electrons in the vicinity of the surface of the sample0 is set to V(x, y)+VB. If the acceleration voltage Va (which value isassumed to be fixed) is smaller than −{V(x, y)+VB}, the electrons willbe the speed components reversal electrons, and will be detected by thedetector 25. On the contrary, if the acceleration voltage Va is largerthan −{V(x, y)+VB}, the electrons will arrive at the surface of thesample 0.

For example, if the acceleration voltage Va=1.6 kV is set up and −1000Vis applied as the bias voltage VB in the example of FIG. 3, the regionS600 of FIG. 3 which is the region where the speed components reversalelectrons which are repelled by the sample surface are not detected isobtained. If the bias voltage VB is set to −850V, the region S750 ofFIG. 3 is obtained as the region where the speed components reversalelectrons are not detected. Alternatively, if the acceleration voltageVa is varied from 1.6 kV to 1.75 kV and the bias voltage VB ismaintained at −1000V, the region S750 can be obtained also.

In addition, when measuring the potential distribution by the conductorpattern in the case where the sample is the electric conduction object,it is possible to use either the method of applying the bias voltage tothe back surface, or the method of applying the bias voltage to thevoltage of the conductor itself.

When changing the threshold of measurement by changing the bias voltageand/or the acceleration voltage while applying the bias voltage, and theelectric charge polarity of the charged particle in the charged particlebeam and the polarity of the surface potential of the sample 0 arereverse polarity, the measurement of the surface potential distributionis attained.

For example, in the case of the surface potential distribution V(x y) ofthe sample >0, the acceleration voltage Va of the electron beam and thebias voltage:VB (<0), depending on whether the condition Va<V(x, y)−VBor the condition Va>V(x, y)−VB is met, it is determined whether thespeed components of the incidence electron in the direction of z arereversed.

Thus, at least one of the acceleration voltage Va and the bias voltageVb is varied in this way, and the threshold of measurement is varied.Measurement of the surface potential distribution is repeatedlyperformed every time the threshold of measurement is varied. Therefore,the whole image (the profile) of the surface potential distribution canbe obtained based on the plurality of measurement results. The result ofcomputation can be easily displayed as a 3-dimensional figure on thedisplay monitor.

In the embodiment of FIG. 5, the case where the direction of incidenceof the charged particle beam which scans the sample 0 in thetwo-dimensional manner is substantially perpendicular to the samplesurface has been explained. Alternatively, the charged particle beam(which is the electron beam in the example of FIG. 5) may be incident tothe scanning region of the sample 0 in a slanting direction to thesample surface.

Also, in such alternative example, the charged particles with which thecomponents vz of the incidence velocity vector in the directionperpendicular to the sample surface are reversed (i.e., the speedcomponents reversal particles), other than the charged particlesincident to the sample surface, can be detected by the detector 25.

In the composition of FIG. 5, the number of the speed componentsreversal particles is varied sensitively to a slight change of the biasvoltage applied to the electric conduction layer 23 a, there is theadvantage for the measurement.

Moreover, the drawing-in voltage of the detector 25 can be made small,and the separation with the secondary electrons generated in the sample0 is easily realized. Furthermore, the threshold of measurement can alsobe changed by changing the degree of the incident angle of the chargedparticle beam to the sample 0. Moreover, the flexibility of the layoutof each part of the measurement device is also increased.

FIG. 6 is a flowchart for explaining the procedure of measuring thelatent-image profile. In the flowchart of FIG. 6, the case where thesurface potential distribution shown in FIG. 3 is made into the latentimage, and the latent-image profile is measured as the profile (V (x, y)of FIG. 3) which is seen from the direction of y (which is perpendicularto the surface of the drawing).

For the sake of convenience of explanation, it is assumed in thisexample that the threshold of measurement is changed by changing thebias potential, and the threshold of measurement is changed in theplurality of N stages.

Upon starting of the procedure of FIG. 6 (step S1), the sample is placedin the measurement device, and the bias potential Vth (j=1) of the 1ststep (j=1) is set by using the parameter j which indicates the number oftimes of measurement as j=1 (step S2).

Then, the acquisition of the contrast image is performed (step S3). Thecontrast image means the region into which the surface potentialdistribution V (x y) is divided for every threshold and for everymeasurement, such as the regions S600 and S750 shown in FIG. 3. Thecontrast image is subjected to the binary processing, and the resultingdigital data is obtained, and it is transferred to the computer which isthe computation unit.

Then, the diameter Dj of the latent image, i.e., the diameter of thecontrast image in the direction of x, is computed based on the receiveddigital data (step S4).

Next, it is determined at step S5 whether the value of the parameter jexceeds the maximum number N of times of measurements (j=N+1 ?).

When the result at the step S5 is negative, the parameter j isincremented (step S6). The control is returned to the above steps S2 toS5, and a new measurement threshold is set up, and the acquisition ofthe contrast image and the calculation of the diameter of the latentimage are performed.

When the result at the step S5 is affirmative, the plurality of valuesof the latent image diameters D1 to DN are obtained in correspondencewith the plurality of measurement thresholds Vth (1) to Vth (N) at the Nstages. Thus, the latent-image profile is computed based on theplurality of measurements results using the computer (step S7).

A description will be given of the detector 25 which is shown in FIG.1A, FIG. 4, and FIG. 5. The detector 25 is formed from a combination ofthe scintillator (phosphor) and the photoelectron multiplier tube. Sincethe speed components reversal electrons repelled by the surfacepotential distribution of the sample 0 have a low energy, they arecaptured by the scintillator with the electric field of the drawing-involtage applied to the surface of the scintillator by the power supplyEA, and converted into the scintillation light by the scintillator. Thescintillation light passes through the light pipe and is amplified intothe current by the photoelectron multiplier tube, so that the currentsignal is taken out as a detection signal.

Usually, the drawing-in voltage applied to the scintillator is about 10kV, and the electric field which is formed near the surface of thesample 0 by the drawing-in voltage is in a range of between 10⁴ and 10⁶V/m. In the region where the electric field by the surface potentialdistribution of the sample 0 is larger, the electrons near the samplesurface tend to be influenced by the electric field by the surfacepotential distribution of the sample 0.

Since the secondary electrons generated on the sample 0 by the electronbeam for scanning the sample 0 have a small energy, most of them arepulled back to the surface of the sample 0, and the ratio of theelectrons captured by the detector 25 is very small.

Especially in the composition of FIG. 5, the detector 25 is arranged onthe side of the sample opposite to the direction of incidence throughthe scanning region where the electron beam is incident to the samplesurface in the slanting direction. The speed components reversalelectrons can be efficiently captured with the composition of FIG. 5,and the ratio of the secondary electrons, generated by the sample 0 andserving as the measurement noise, captured by the detector 25 can bereduced further, and the S/N ratio of measurement can be raised.

Alternatively, it is possible to use the micro channel plate (MCP)instead of the scintillator. When using MCP, it is possible to collectthe current and amplify the electron captured by MCP by the currentcollection electric field by which it was applied in the input side ofthe MCP, and it is possible to increase by the thousands times, and thegood detection signal can be acquired.

By using the above-described embodiment, the surface potentialdistribution measurement method can be realized. In the measurementmethod, the sample 0 having a surface with a surface potentialdistribution is scanned using a charged particle beam in atwo-dimensional manner. A detection signal is obtained by thetwo-dimensional scanning to measure the surface potential distributionof the sample 0. The charged particles, other than charged particles ofthe charged particle beam incident to the sample surface by thetwo-dimensional scanning, with which the components vz of an incidencevelocity vector of the charged particles in a direction perpendicular tothe sample surface are reversed, are detected so that a detection signalindicating an intensity according to the detected charged particles isobtained in correspondence with a position on the sample surface.

Moreover, a uniform bias potential may be applied to the surface of thesample with respect to the surface-potential distribution in theabove-mentioned measurement method by using the embodiments shown inFIG. 3 and FIG. 4. Moreover, the uniform bias potential VB applied tothe surface of the sample with respect to the surface-potentialdistribution may be varied, and every time the bias potential VB isvaried, the surface potential distribution is measured, so that aprofile of the surface potential distribution is computed based on aplurality of measurement results thus obtained.

Moreover, in the above-mentioned measurement method, an accelerationvoltage Va applied to create the charged particle beam for thetwo-dimensional scanning of the sample 0 may be varied, and every timethe acceleration voltage Va is varied the surface potential distributionis measured, so that a profile of the surface potential distribution iscomputed based on a plurality of measurement results thus obtained.

Moreover, in the above-mentioned measurement method, at least one of theuniform bias potential VB applied to the sample surface with respect tothe surface potential distribution and the acceleration voltage Vaapplied to create the charged particle beam for the two-dimensionalscanning of the sample may be varied, and every time the at least one ofthe uniform bias voltage VB and the acceleration voltage Va is variedthe surface potential distribution is measured, so that a profile of thesurface potential distribution is computed based on a plurality ofmeasurement results thus obtained.

Moreover, in the above-mentioned measurement method, an electron beammay be used as the charged particle beam for the two-dimension scanningto the sample 0 having the surface with the surface potentialdistribution. Alternatively, in the above-mentioned measurement method,an ion beam may be used as the charged particle beam for thetwo-dimension scanning to the sample having the surface with the surfacepotential distribution.

Moreover, by using the above embodiment of FIG. 5, the charged particlebeam may be incident to the scanning region of the sample 0 having thesurface with the surface potential distribution in a slanting directionto the sample surface.

Furthermore, by using the above-described embodiment of FIG. 1A, thesurface potential distribution measurement device can be realized. Thismeasurement device comprises the charged particle beam scanning unit(the elements 10 to 21 in FIG. 1A), the capture unit 25, and themeasurement unit (such as the computer not illustrated). The chargedparticle beam scanning unit scans the sample 0 having a surface with asurface potential distribution using a charged particle beam in atwo-dimensional manner. The capture unit 25 captures the chargedparticles, other than the charged particles of the charged particle beamincident to the sample surface by the two-dimensional scanning, withwhich the components of an incidence velocity vector of the chargedparticles in a direction perpendicular to the sample surface arereversed. The measurement unit obtains a detection signal indicating anintensity according to the captured charged particles in correspondencewith a position on the sample surface, so that the surface potentialdistribution is measured with the detection signal.

Moreover, by using the embodiments of FIG. 4 and FIG. 5, theabove-mentioned measurement device may further comprise a bias potentialapplication unit (the support part 23A and the power supply EB) whichapplies a uniform bias potential to the surface of the sample 0 withrespect to the surface potential distribution. Moreover, theabove-mentioned measurement device may further comprise a bias potentialvarying unit EB which varies the bias potential applied by the biaspotential application unit, and a computation unit (for example, thecomputer which is not illustrated) which computes the profile of thesurface potential distribution based on the plurality of measurementresults which are obtained by measuring the surface potentialdistribution every time the bias potential is varied.

Moreover, the above-mentioned surface potential distribution measurementdevice may further comprise an acceleration voltage varying unit (forexample, the accelerator provided in the electron gun 10) which variesthe acceleration voltage applied to create the charged particle beam forthe two-dimensional scanning, and a computation unit (for example, thecomputer which is not illustrated) which computes the profile of thesurface potential distribution based on the plurality of measurementresults which are obtained by measuring the surface potentialdistribution every time the acceleration voltage is varied.

Moreover, by using the embodiments of FIG. 4 and FIG. 5, theabove-mentioned measurement device may further comprise the biaspotential varying unit (the power supply EB) which varies the uniformbias potential applied to the sample surface by the bias potentialapplication unit (the support part 23A and the power supply EB).Moreover, the above-mentioned measurement device may further comprise acomputation unit (for example, the computer which is not illustrated)which computes the profile of the surface potential distribution basedon the plurality of measurement results which are obtained by measuringthe surface potential distribution every time the bias potential and/orthe acceleration voltage is varied.

Moreover, as described above, in the above-mentioned measurement device,the electron gun 10 which generates an electron beam may be provided sothat the electron beam is used as the charged particle beam for thetwo-dimensional scanning to the sample 0 having the surface with thesurface potential distribution. Moreover, in the above-mentionedmeasurement device, a liquid-metal ion gun which generates an ion beammay be provided so that the ion beam is used as the charged particlebeam for the two-dimensional scanning to the sample 0 having the surfacewith the surface potential distribution.

Moreover, by using the embodiment of FIG. 5, in the above-mentionedmeasurement device, the charged particle beam scanning unit may bearranged so that the charged particle beam is incident to the scanningregion of the sample having the surface with the surface potentialdistribution, and the capture unit 25 provided in the measurement unitmay be arranged through the scanning region on the side opposite to thedirection of incidence of the charged particle beam.

Moreover, in the above-described measurement method, the sample may bean electrophotographic photoconductor, and the surface potentialdistribution of the sample may be measured as a surface potentialdistribution concerning an electrostatic latent image formed on thephotoconductor. Next, a description will be given of the above case.

As previously described in the foregoing, the electrophotographicphotoconductor has the tendency of the dark decaying, and the time inwhich the electrostatic latent image formed on the photoconductor can bemeasured is only about dozens seconds. For this reason, when the sample0 is the electrophotographic photoconductor, the electrostaticlatent-image formation unit must be arranged in the sealed casing 30.

FIG. 7 shows the composition of the surface potential distributionmeasurement device in the preferred embodiment of the invention, whichincludes the electrostatic latent-image formation unit.

In FIG. 7, the electron gun 10, the beam monitor 13, the condenser lens15, the aperture 17, the beam blanker 18, the scanning lens 19, theobjective lens 21, and the support part 23 are essentially the same ascorresponding elements in FIG. 1A, and a description thereof will beomitted for the sake of convenience.

In addition, the electron gun 10, the beam monitor 13, the condenserlens 15, the aperture 17, the beam blanker 18, the scanning lens 19, andthe objective lens 21 constitute the charged particle beam irradiationunit 11A, the respective components of the charged particle beamirradiation unit 11A are controlled by the charged particle beam controlunit 31, and the charged particle beam irradiation unit 11A and thecharged particle beam control unit 31 constitute the charged particlebeam scanning unit.

In the present embodiment, the sample 0 is the electrophotographicphotoconductor, the back surface of the sample 0 is supported by theupper surface of the conductive support part 23, and the conductivesupport part 23 is grounded.

Moreover, in FIG. 7, the reference numeral 34 denotes the semiconductorlaser which is the light source, the reference numeral 35 denotes thecollimator lens, the reference numeral 36 denotes the aperture, thereference numeral 37 denotes the mask, and the reference numerals 38, 39and 40 denotes the lenses which constitute the imaging lens. Theseelements constitute the image irradiation unit, and the imageirradiation unit, the semiconductor laser control unit 33 and the imageirradiation control unit which is not illustrated constitute theexposure unit.

The image irradiation control unit which is not illustrated is capableof performing the focusing and magnification conversion by adjustment ofthe positional relation between the imaging lenses 38, 39 and 40 and themask 37.

In FIG. 7, the reference numeral 25 denotes the detector (the captureunit), 26 denotes the signal processing unit, 26A denotes the monitor,and 28 denotes the output device, such as the printer, respectively. Thedetector 25, the signal processing unit 26, the monitor 26A, and theoutput device 28 constitute the measurement unit. In addition, thereference numeral 29 denotes the light emitting device for electricerasing.

As shown in FIG. 7, the respective parts of the above-mentionedmeasurement device are accommodated in the casing 30, and the inside ofthe casing 30 can be decompressed to the substantially vacuum state byusing the suction unit 32. That is, the casing 30 functions as a vacuumchamber.

Moreover, the whole measurement device is controlled by the hostcomputer 45 (which is the control unit controlling the measurementdevice synthetically). The charged particle beam control unit 31 and thesignal processing unit 26 may be incorporated in the host computer 45 asa part of the function.

In the condition shown in FIG. 7, the sample 0 having the uniformlycharged surface is placed on the support part 23, and the inside of thecasing 30 is decompressed to the substantially vacuum state.

In such condition, the semiconductor laser 34 is turned on and the imageof the mask 37 is focused on the uniformly changed surface of the sample0. The pattern of the electrostatic latent image according to the imageirradiated to the sample 0 by this exposure is formed.

Thus, the surface in which the pattern of the electrostatic latent imageis formed is scanned in a two-dimensional manner by the electron beam,and the speed components reversal electrons repelled by the barrierpotential generated by the surface potential of the sample 0 arecaptured by the detector 25. A detection signal indicating the intensityaccording to the captured electrons outputted by the detector 25 isobtained and converted into the electric signal.

Similar to the previous embodiment, the acceleration voltage Va isvaried, and every time the acceleration voltage Va is varied themeasurement is repeated, so that the latent-image profile of theelectrostatic latent image can be computed by the signal processing unit26 which is the computation unit controlled by the host computer 45. Theresult of the computation from the signal processing unit 26 isoutputted to the output device 28.

In order to form the pattern of the electrostatic latent image on thesample 0 which is the photoconductive sample, the surface of the sample0 must be charged uniformly prior to the exposure of the image.

In the embodiment of FIG. 7, charging by the electron beam is performedon the sample surface using the charged particle beam scanning unit 11A.

Namely, if the electron beam is irradiated to the sample 0, thesecondary electron will occur from the photoconductive sample SP withthe impact of the irradiated electron. However, if the ratio of theamount R1 of the electrons irradiated to the sample 0 to the amount R2of the secondary electrons discharged is larger than 1, the amount ofthe electrons irradiated exceeds the amount of the secondary electronsdischarged. The difference between the amount R1 and the amount R2 isaccumulated in the photoconductive sample SP, and the surface of thesample 0 is thus charged.

Therefore, the quantity and acceleration voltage of the electronsemitted from the electron gun 10 are adjusted, and the condition inwhich the ratio R1/R2 is larger than 1 is set up, and thetwo-dimensional scanning of the electron beam is applied to the sample0. Thus, uniform charging of the surface of the sample 0 can be carriedout.

Such adjustment of the amount of the discharge electrons and theacceleration voltage is carried out by using the charged particle beamcontrol unit 31.

Moreover, switching on and off of the irradiation of the electron beamin accordance with the scanning of the electron beam is performed bycontrolling the beam blanker 18 by the charged particle beam controlunit 31.

As an alternative charging unit, the contact charging, the pouringcharging, and the ion irradiation charging may also be used instead.

FIG. 8 shows the state where the surface of the sample 0 is charged bythe electron beam as described above.

It is called function separated photoconductor to be shown in FIG. 8 asa sample 0 which is the photoconductive sample, it forms the electriccharge generation layer 2 on the electric conduction layer 1, and formsthe electric charge transportation layer 3 on it.

The electron irradiated by the electron gun 10 is fired into the surfaceof the electric charge transportation layer 3, is captured by theelectron course of the electric charge transportation layer materialmolecule in the surface of the electric charge transportation layer 3,and where the molecule is ionized, it stops at the surface unit of theelectric charge transportation layer 3.

This state is in the state where the sample 0 was charged.

Thus, if the exposure light is irradiated by the sample 0 in the statewhere it is charged, the irradiated light will penetrate the electriccharge transportation layer 3, will result in the electric chargegeneration layer 2, and will generate the positive and negative electriccharge carrier in the electric charge generation layer 2 by the energy.

The negative carrier moves to the electric conduction layer 1 among thegenerated positive and negative electric charge carriers in the actionof the restitution by the minus electric charge of the surface of theelectric charge transportation layer 3, and the electric chargetransportation layer 3 is conveyed to the right carrier, and it sets offagainst the minus electric charge (captured electron) of the surfaceunit of this layer 3, and suits.

Thus, in the portion irradiated with the exposure light in the sample 0,the charging electric charge and the potential distribution according tothe intensity distribution of the exposure light is formed.

The surface potential distribution by the pattern of this potentialdistribution is the pattern of the electrostatic latent image, and it isthe candidate for measurement.

As described above, the image is exposed to the uniformly chargedsurface of the sample 0 and the pattern of the electrostatic latentimage is formed. The above-mentioned exposure unit (FIG. 7) carries outthis exposure. That is, the semiconductor laser 34 is turned on and theimaging of the mask 37 to the surface of the sample 0 is carried out bythe action of the imaging lenses 38, 39, and 40.

The semiconductor laser 34 which has a luminescence wavelength in thewavelength region where the sample 0 is sensitive is used. Since theexposure energy is equal to the time quadrature of the optical power onthe surface of the sample 0, the lighting time of the semiconductorlaser 34 is controlled by the LD control unit 33. In this way, theexposure at the desired exposure energy on the sample 0 can be carriedout.

FIG. 9 shows an example of the irradiation of the optical image to thephotoconductive sample surface by the image irradiation unit in thesurface potential distribution measurement device of FIG. 7.

In FIG. 9, the reference numeral 34 denotes the semiconductor laserwhich is the light source, the reference numeral 35 denotes thecollimator lens, the reference numeral 36 denotes the aperture, and thereference numeral 37 denotes the mask, respectively. The referencenumeral 38A denotes the imaging lens which includes the three lenses 38,39 and 40 as in FIG. 7.

The light beam emitted from the semiconductor laser 34 is converted intothe parallel light beam by the collimator lens 35, and the diameter ofthe light beam is regulated by the aperture 36, so that the light beamis incident to the mask 37.

With the light beam which passes through the mask 37, the image of themask pattern in the mask 37 is focused on the image surface by theaction of the imaging lens 38A. In the present embodiment, the imagesurface is the uniformly charged surface of the sample 0 laid on thesupport part 23.

In this way, the exposure of the sample 0 is performed and the patternof the electrostatic latent image corresponding to the mask pattern isformed on the surface of the sample 0.

As shown in FIG. 9, if the object distance of the mask 37 in the imaginglens 38A is set to L1 and the image distance is set to L2, the imagingmagnification (beta) in the direction perpendicular to the optical axisof the imaging lens 38A is L2/L1, and the imaging of the mask patternimage according to this magnification will be carried out.

The imaging lens 38A is arranged so that the mask 37 and the surface ofthe photoconductive sample may serve as the conjugate. Since the imagingmagnification beta and the size of the mask pattern are knownbeforehand, the size of the mask pattern image formed on the surface ofthe photoconductive sample can be computed. Thus, it is possible to formthe desired electrostatic latent-image pattern on the surface of thephotoconductive sample.

In order to set up the optical path for exposure in the exposure unitoutside the region where the charged particle beam for thetwo-dimensional scanning of the photoconductive sample passes, theoptical axis of the imaging lens 38A is inclined to the normalperpendicular to the uniformly charged surface of the photoconductivesample.

Therefore, as shown in FIG. 9, the mask 37 is also inclined to theoptical axis of the imaging lens 38A, and the image of the mask patternwith the imaging lens 38A is arranged so that it matches with thesurface of the photoconductive sample.

The inclination angles alpha and theta of the mask 37 and thephotoconductive sample surface to the optical axis of the imaging lens38A are respectively set up as alpha=theta=45 degrees in the presentembodiment. This is because the imaging magnification beta (=L2/L1) inthe present embodiment is equal to 1 (L1=L2).

In the present embodiment, the image of the mask pattern formed on thesurface of the photoconductive sample is magnified by the square root of2 on the surface parallel to the drawing in the direction perpendicularto the drawing of FIG. 9, and the mask pattern can be designed by takinginto consideration this.

In the general case where the imaging magnification is not equal to 1,the equation: L1 tan(alpha)=L2 tan(theta) where L1 is the objectdistance, L2 is the image distance, alpha is the inclination angle ofthe mask, and theta is the inclination angle of the sample surface,should be considered.

The mask pattern in the mask 37 is the mask pattern for resolutioninspection. In the present embodiment, the mask pattern is also thenegative pattern, the portion corresponding to the portion by whichoptical irradiation is carried out on the occasion of formation of theelectrostatic latent image is light-transmission nature, and otherportions are shading nature so that the negative latent image can beformed in photoconductivity data.

In order to lean to FIG. 7 in the surface potential distributionmeasurement device in which the present embodiment is shown to thenormal which the optical axis of the imaging in the exposure unit stoodto the surface of the sample 0 and to make parallel the image of themask 37 by which the imaging is carried out on the sample surface forthis reason, the device for inclining the mask 37 to the optical axis isrequired.

As shown in FIG. 5, in setting up the irradiation direction of thecharged particle beam with inclination to the sample surface, similar tothe embodiment of FIG. 10, the collimator lens 35 from the semiconductorlaser 34, the mask 37A, the surface of the sample 0 and the optical pathwhich reaches the surface of the sample 0 through imaging lens 38A canbe made to be able to cross at right angles, the surface of the sample 0can be made to be able to carry out the imaging of the image of mask 37Aby imaging lens 38A, and mask 37A can be installed in the sample surfaceand parallel in this case.

FIG. 11 shows the composition of the surface potential distributionmeasurement device in another preferred embodiment of the inventionwhich measures the electrostatic latent image formed in thephotoconductor of photoconductivity.

In FIG. 11, the elements which are essentially the same as correspondingelements in FIG. 1 and FIG. 7 are designated by the same referencenumerals, and a description thereof will omitted for the sake ofconvenience of description.

The electron gun 10 and the aperture 13 which constitute the chargedparticle beam irradiation unit 11A, the condenser lens 15, the aperture17, the beam blanker 18, the scanning lens 19, and the objective lens 21are the same as the corresponding elements in FIG. 1 and FIG. 7. Thedetector 25 and the signal processing unit which is not illustrated arethe same as corresponding elements which are described above with FIG.7. In FIG. 11, the reference numeral 30A denotes the casing.

The sample 01 which is the electrophotographic photoconductor is formedin the shape of a drum, and uniform rotation is carried out in thedirection of the arrow (counterclockwise rotation) by the drive unitwhich is not illustrated.

After the sample 01 is set in the casing 30A, the inside of the casing31A is highly decompressed by the suction unit which is not illustrated.

The charging unit 42 is a contact-type charging unit which includes, forexample, the charging brush, the charging roller, etc., and carries outcontact charging of the sample 01 uniformly within the casing underpressure reduction.

At this time, uniform rotation of the sample 01 is carried out in thedirection of the arrow (counterclockwise rotation). As described abovewith FIG. 7, the sample 01 can also be charged by using the electronbeam.

The exposure unit 41 carries out exposure by irradiating the opticalimage to the uniformly charged surface of the sample 01.

The image can be irradiated by the optical writing using the knownoptical scanning device in the laser printer etc. as the exposure unit41.

Thus, if the image is irradiated in the optical writing, the form of thepattern of the electrostatic latent image formed in the writing can bechanged arbitrarily, and the pattern of the request of the electrostaticlatent image can be formed easily.

In addition, when installation into the casing 31A is difficult, theoptical scanning device is formed in the exterior of the casing 31A, thetransparent window unit is prepared in the casing 31A, and it may bemade for the optical scanning device to become large when using theoptical scanning device as the exposure unit 41, and to irradiate theimage from the outside to the photoconductive sample 01 through thiswindow unit.

Although the scan of the electron beam by the charged particle beamirradiation unit 11A may be performed by deflecting the electron beam intwo-dimensional manner similar to the embodiments of FIG. 1 and FIG. 7,since the scan is received the sample 01 carrying out uniform rotationin the direction of the arrow, the electron beam can be deflected in onedimension in the direction which intersects perpendicularly with thedrawing, and the two-dimensional scanning can also be realized combiningthis deviation and rotation of the sample 01.

As described in the foregoing, by using the embodiments of FIG. 7 toFIG. 11, the surface potential distribution measurement device can berealized. In the measurement device, the measurement sample may be anelectrophotographic photoconductor, and the surface potentialdistribution of the sample is measured as a surface potentialdistribution concerning an electrostatic latent image formed on thephotoconductor, wherein the measurement device comprises the chargingunit 11A charging the photoconductor uniformly, and the exposure unitirradiating an optical image to the uniformly charged photoconductor.

Moreover, by using the embodiments of FIG. 7 and FIG. 10, the exposureunit in the above-mentioned measurement device may be provided to carryout projection exposure of the mask patterns 37 and 37A. Moreover, byusing the embodiment of FIG. 7, the above-mentioned measurement devicemay be provided so that the optical path for exposure is arrangedoutside the region which the charged particle beam passes through forthe two-dimensional scanning of the photoconductor performed by theexposure unit.

Moreover, by using the embodiment of FIG. 11, in the surface potentialdistribution measurement device, the exposure unit 41 may be provided tooptically write an electrostatic latent image pattern to thephotoconductor by the two-dimensional scanning.

Moreover, by using the embodiments of FIG. 7 to FIG. 11, the exposureunit in the above-mentioned measurement device may be provided toinclude the semiconductor laser 34 which is used as a light source forthe exposure. Moreover, by using the embodiments of FIG. 7 to FIG. 11,the exposure unit in the above-mentioned measurement device may beprovided so that an exposure time of the exposure unit is controllable.

Moreover, by using the embodiments of FIG. 7 and FIG. 10, in the surfacepotential distribution measurement device, the charged particle beamscanning unit 11A may be provided to charge the photoconductor sample 01uniformly by using an electron beam for the two-dimensional scanning,and to serve as the charging unit of the photoconductor sample 01.

Next, FIG. 15 shows the composition of the surface potentialdistribution measurement method and device in another preferredembodiment of the invention, in which the charged particle irradiationunit, the sample installation unit, and the secondary electron detectingunit are provided.

As shown in FIG. 15, the surface potential distribution measurementdevice in this embodiment comprises the charged particle irradiationunit 50 which irradiates the charged particle beam, the sampleinstallation unit 60, and the secondary electron detecting unit 70.

In addition, the connection of the sample and the electrode in thesample installation unit 60 shown in FIG. 14 is illustrated notionally,and a description thereof will be given later (see FIG. 16 or FIG. 17).

Each of the respective components is arranged in the same chamber 90,and the chamber 90 is maintained in the vacuum at the time ofmeasurement.

Moreover, the charged particles in this embodiment mean the particlesthat are influenced by the electric field or the magnetic field, such asthe electron beam or the ion beam. Hereafter, the preferred embodimentwhich irradiates the electron beam will be explained.

The charged particle irradiation unit 50 (which is the electron beamirradiation unit in the present embodiment) comprises the electron gun51 for generating the electron beam, the beam monitor 52 for monitoringthe electron beam generated by the electron gun 51, the capacitor lens53 for converging the electron beam, the aperture 54 for controlling theirradiation current of the electron beam, the beam blanker 55 forswitching on and off the irradiation of the electron beam, the scanninglens (deflecting coil) 56 for scanning of the electron beam from thebeam blanker 55, and the objective lens 57 for focusing the electronbeam from the scanning lens 56 again. The power supply for driving ofeach lens which is not illustrated is connected to each of therespective lenses.

In FIG. 15, the reference numeral 61 denotes the grid mesh electrode, 62denotes the sample, 63 denotes the conductor (conductive material), 66denotes the power supply, and 71 denotes the secondary electrondetector, respectively.

In addition, when installing the sample on the sample support part, itis desirable to insert the insulator so that the back surface of thesample may not be grounded.

Moreover, the charged particle irradiation unit 50 has also the functionas the charging unit for charging of the sample (photoconductor etc.) aswell as the function of measurement of the electrostatic latent image.

Moreover, the exposure unit which includes the optical system may beprovided in the composition of the surface potential distributionmeasurement device as in the following embodiment (FIG. 22).

The scintillator, the photo multiplier tube, etc. are used in thesecondary electron detector 71 of the secondary electron detecting unit70. On the other hand, in the case of the ion beam being used, theliquid-metal ion gun can be used instead of the electron gun.

FIG. 16 shows an example of the connection of the sample 62 (forexample, photoconductor) and the electrode installed in the sampleinstallation unit 60 in the surface potential distribution measurementdevice of the present embodiment.

The conductor (conductive material) 63 to which the voltage is appliedis arranged on the back surface of the sample 62, and the grid meshelectrode 61 which is made of the conductive member is arranged abovethe sample 62. The conductor (conductive material) 63 may be a part ofthe sample itself.

Moreover, the grid mesh electrode 61 is grounded. The power supply 66 isthe power supply which is capable of generating a high voltage in theorder of several tens kV. The power supply 66 is provided so that it canset up arbitrarily the voltage value.

In FIG. 16, the potential (V1) of the back surface of the sample 62 isequal to the applied voltage (Vin). That is, assuming that V1 (=Vin) isthe potential of the back surface of the sample 62, V2 is the potentialof the front surface of the sample 62, V3 is the potential of the gridmesh electrode 61, and d is the distance between the sample 62 frontsurface and the grid mesh electrode 61, the average electric fieldintensity E that is generated between the sample 62 and the grid meshelectrode 61 is approximately represented by the following formulas:E=(V3−V2)/d,V2=V1+Vc

where Vc is the equivalent for the potential accompanied with thecharging electric charge. Therefore, the average electric fieldintensity E may be varied by varying the V1.

If the potential V3 of the grid mesh electrode is set to 0V or thepotential near zero volt even when V1 is a high voltage which is equalto the acceleration voltage of the incidence electron, it is possible tocontrol the influences on the incidence electron course. Moreover, it isalso possible to change the sample electric field.

In this way, by arranging the grid mesh electrode as a conductive memberfor applying voltage, the bias component of the electric field intensitycan be changed without interrupting the incidence charged particle beam(for example, the electron beam), and the problem, such as the bendingof the incidence electron beam, can be overcome.

FIG. 17 shows another example of the connection of the sample and theelectrode in the sample installation unit in the surface potentialdistribution measurement device of the present embodiment.

As shown in FIG. 17, in this composition, the insulator 64 is insertedbetween the back surface of the conductor (conductive material) 63 asshown in FIG. 16 and the sample support part 65.

In addition, the conductor (conductive material) 63 may be a part of thesample itself. Generally the sample support part 65 is grounded. Forthis reason, when the sample 62 lower part is made of the conductivematerial, it is desirable to insert the insulating material, such as aplastic resin, as the insulator 64 between the sample support part 65and the sample 62. Thereby, the potential bias component can be variedso that the desired electric field intensity is obtained.

It is desirable that the grid mesh electrode 61 according to theinvention is made of the conductive material, such as aluminum orstainless steel, and it is the non-magnetism or weak magnetism whichdoes not affect the course of the incidence charged particles (electronetc.).

Without affecting the course of the incidence charged particle beam (forexample, electron beam) by using the nonmagnetic substance, thepotential bias component can be changed so that the desired fieldintensity is obtained, and the surface potential distribution can bemeasured correctly.

Moreover, FIG. 18A to FIG. 18C show some examples of the grid meshelectrode which is arranged above the beam incidence side surface of thesample.

As shown, any of the normal grid mesh electrode (FIG. 18A), the gridmesh electrode with hole (FIG. 18B), and the hole plate (FIG. 18C) maybe used as the grid mesh electrode according to the invention.

Such grid mesh electrodes are suitable because they do not interrupt theincidence charged particles (for example, electrons), and can shift thebias level of the electric field distribution uniformly. The pitch andform of the grid mesh are decided according to the measurement subjector imaging magnification, and the grid mesh electrode can be madesuitable and can be used properly.

On the other hand, the bias component of the electric field intensity inthe sample surface can be shifted to the desired value by applying thebias voltage to the sample upper surface.

For example, what is necessary is just to arrange the grid meshelectrode 1 mm above the upper part of the sample surface, and to applythe voltage of −2000V to the lower electrode of the sample surface, inorder to shift the field intensity of 2×10⁶ V/m as the bias component.

FIG. 19A and FIG. 19B are diagrams for explaining notionally thedifference in the contrast image between the case where there is nofield intensity bias (FIG. 19A) and the case where there is the biaselectric field (Eb) applied (FIG. 19B).

As shown in FIG. 19A and FIG. 19B, the light and darkness are made bythe contrast image on bordering on the field intensity of Eb before thebright portion increases and carries out the bias shifting as a resultof the electric field bias shifting.

Accordingly, since the portion of the electric field intensity E=Eb inthe original state is set to E=0 by the bias shifting, it is possible toobtain the electrostatic latent-image distribution of the approximatelybinary image by setting that electric field intensity to the thresholdlevel. By carrying out the image processing of the measurement result,the diameter of the latent image can be computed.

According to the present embodiment, the contrast image when setting anarbitrary electric field intensity to the threshold level is obtained bychanging the potential bias and the electric field intensity formed onthe sample surface as mentioned above.

Moreover, the measurement in which the potential bias component Eb ofthe electric field intensity is varied to the sample upper surface isrepeated for a plurality of times, and it is possible to compute thelatent-image profile (the profile of the electrostatic latent-imagedistribution) of the surface potential distribution by acquiring thedata (latent-image data) and carrying out computation processing of theobtained data on the computer.

FIG. 20 shows the procedure which computes the latent-image profile ofthe surface potential distribution (electrostatic latent-imagedistribution) based on the plurality of measurement results which areobtained by measuring the surface potential distribution repeatedlyevery time the electric field intensity is varied (the value of Eb isvaried N times).

Upon starting of the procedure of FIG. 20, the sample is placed in themeasurement device, and the bias potential Eb (i=1) of the 1st step(i=1) is set by using the parameter i which indicates the number oftimes of measurement as i=1 (step S101).

Then, the acquisition of the contrast image is performed (step S102).The contrast image means the region into which the surface potentialdistribution is divided for every threshold and for every measurement.The contrast image is subjected to the binary processing, and theresulting digital data is obtained, and it is transferred to thecomputer which is the computation unit (step S103).

Then, the diameter Di of the latent image, i.e., the diameter of thecontrast image in the direction of x, is computed based on the receiveddigital data (step S104).

Next, it is determined at step S105 whether the value of the parameter iexceeds the maximum number N of times of measurements (i=N ?).

When the result at the step S105 is negative, the parameter i isincremented (step S106). The control is returned to the above steps S101to S105, and a new measurement threshold is set up, and the acquisitionof the contrast image and the calculation of the diameter of the latentimage are performed.

When the result at the step S105 is affirmative, the plurality of valuesof the latent image diameters D1 to DN are obtained in correspondencewith the plurality of measurement thresholds Eb (1) to Eb (N) at the Nstages. Thus, the latent-image profile is computed based on theplurality of measurements results using the computer (step S107).

Furthermore, there is the method of changing the drawing-in voltage ofthe detector as another method of changing the bias component of theelectric field intensity.

The secondary electron detector is prepared in the secondary electrondetecting unit of the present invention. Since the secondary electronwhich this secondary electron detector combined the scintillator(phosphor) and the photoelectron multiplier tube, and was generated fromthe sample detected has low energy, it accelerates under the influenceof the electric field of the high voltage applied on the surface of thescintillator, and it is changed into light.

Through the light pipe, with the photoelectron multiplier tube (PMT),this light is amplified as the current and taken out as a currentsignal.

As mentioned above, in the present invention, secondary electronicimages are observable by irradiating and scanning the electron beam onthe sample, for example.

Usually, the drawing-in voltage from the scintillator is about 10 kV,and the electric field near the sample is only about 1×10⁴-10⁵ V/m. Forthis reason, when the electric field generated by the potentialdistribution of the sample is larger, it is easy to be influenced of thesample electric field.

Therefore, the bias component of the electric field intensity ischangeable by enlarging the drawing-in voltage of the detector orbringing the detector close to the sample.

The profile of the electrostatic latent-image distribution can bemeasured by repeating the measurement in which the bias component of theelectric field intensity on the sample upper surface is varied two ormore times.

Moreover, the bias shifting of the electric field intensity can also bemore effectively realized by a combination of enlarging of thedrawing-in voltage of the detector and bringing of the detector close tothe sample.

Moreover, it is possible to use the MCP (micro channel plate) instead ofthe scintillator. The current is collected by the current collectionelectric field applied to the input side of MCP, the secondary electroninputted into MCP is amplified, and it is increased by the thousandstimes. The signal components of the secondary electron is increasedsharply and such amplification enables it to raise the S/N ratio of theimage signal.

According to the measuring method and device of the surface potentialdistribution of the present embodiment, the potential bias component ofthe sample and the electric field intensity formed on the sample surfaceare varied, the contrast image in which the arbitrary field intensity isset to the threshold level can be obtained, and the electric fielddistribution in the vertical direction near the sample surface which isformed by the surface potential distribution or its potentialdistribution of the dielectric-substance sample can be measured withhigh resolution.

By measuring the electrostatic latent image of the photoconductor, itbecomes possible to improve the process quality and improvement inquality, such as high resolution, the raise in the durability, highstabilization, and energy saving, can be attained.

In the present embodiment, while making easy device composition ofsurface potential distribution measurement by using the electron beam asa charged particle beam to irradiate, it is easy to consider as thesuitable composition for electrostatic latent-image measurement of theelectrophotographic photoconductor.

Next, an example of the method of forming the electrostatic latent imagein the photoconductor sample will be described. FIG. 21 shows thecomposition of the principal part of the photoconductor.

As shown in FIG. 21, the photoconductor usually comprises the electriccharge generation layer (CGL) 2 and the electric charge transportationlayer (CTL) 3 on the electric conduction layer (conductive supportobject) 1.

When exposure is carried out in the state where the electric charge(surface electric charge 4) is charged on the surface of thephotoconductor of FIG. 21, light will be absorbed by the electric chargegeneration material (CGM) of the electric charge generation layer (CGL)2, and the charge carriers of positive/negative polarity will occur.

One side of the carriers is poured into the electric chargetransportation layer (CTL) 3, and the other side is poured into theelectric conduction layer 1 by the electric field. By the electricfield, the carriers poured into the electric charge transportation layer3 move even to the CTL surface, combines the inside of CTL with thesurface electric charge 4 of the photoconductor, and disappears. Thisforms the potential distribution of the electrostatic latent image onthe photoconductor surface.

Specifically, the surface of the photoconductor will be charged byirradiation of the electron beam to the photoconductor. The accelerationvoltage E1 in this case is set to an acceleration voltage higher thanthe acceleration voltage E0 at which the ratio (delta) of thesecondary-electron-emission from the surface of the photoconductor isset to 1.

Thus, when the setting occurs, the amount of incidence electrons mayexceed the amount of discharge electrons, the electron is accumulated onthe photoconductor and the excessive charging occurs. Consequently, thesample can be charged to the negative polarity. The desired chargingpotential can be formed by setting the acceleration voltage and theirradiation time appropriately.

Next, the exposure of the charged photoconductor is performed using theexposure unit including the optical system, and the electrostatic latentimage is measured.

FIG. 22 shows the composition of the surface potential distributionmeasurement device in another preferred embodiment of the inventionwhich can carry out the charging, the exposure, and the electrostaticlatent-image measurement.

The charged particle irradiation unit 50 of FIG. 22 has the function asthe charging unit which electrifies the sample other than themeasurement function of the surface potential distribution, as describedabove with FIG. 14.

And the exposure unit 80 of FIG. 22 includes the light source 81 whichhas sensitivity about the photoconductor, the collimator lens 82, theaperture 83, the imaging lens 84, etc., and it is possible to create thedesired beam diameter and the beam profile on the sample 62 installed inthe sample installation unit 60.

Moreover, the suitable exposure time and exposure energy can beirradiated by the LD control unit as described below.

In order to form the pattern of the line, it is possible to attach thescanning mechanism which uses the galvano mirror and the polygon minorfor the optical system.

FIG. 23 shows the composition of the respective control units used inthe embodiment of FIG. 22.

As shown in FIG. 23, there are provided the LD control unit 131 whichcontrols the light source 81, the charged particle control unit 132which controls the scanning lens 56, the LED control unit 133 whichcontrols the light source 139 for electric charge erasing, and thesample support part control unit 134 which controls movement of thesample support part 130. The LD control unit 131, the charged particlecontrol unit 132, the LED control unit 133, and the sample support partcontrol unit 134 are controlled by the host computer 135.

Moreover, the output of the secondary electron detector 71 is detectedby the secondary electron detecting unit 136, and this detection signalis processed by the signal processing unit 137 and the secondaryelectronic measurement result is outputted from the measurement resultoutput unit 138.

Furthermore, FIG. 24 shows the composition of the surface potentialdistribution measurement device (photoconductor electrostaticlatent-image distribution measurement device) in the preferredembodiment which enables measurement when the sample is in thecylindrical form.

Especially the embodiment that enables the measurement of thecylindrical form sample is suitable for the non-destructive measurementof the electrostatic latent image on the electrophotographicphotoconductor on the practical application level.

As shown in FIG. 24, in the one chamber 90, in order to measure theexposure unit 141 for exposing the charging unit 142 for forming thepotential distribution in the surface of the sample (photoconductor) 140which includes the cylindrical form, and the photoconductor 140, and thecharged sample surface, and the potential distribution, the chargedparticle irradiation unit 50 (the present embodiment electron beamirradiation unit) which irradiates and scans the charged particle, andthe detecting element 144 which detects the secondary electron whichcreated are arranged.

In addition, the electric discharge unit 143 for electric discharge ofthe residual charge is formed.

The electron beam irradiation unit 50 is similarly comprised with thatshown in FIG. 15 or FIG. 22 from the electron gun 51, the beam monitor52, the capacitor lens 53, the aperture 54, beam blanker 55, thescanning lens (deflecting coil) 56, and the objective lens 57. The powersupply for the drive which is not illustrated is connected to each lens.

The secondary electron detector, such as the scintillator and the photomultiplier tube, is used for the detecting element 144 of the secondaryelectron.

In addition, when irradiating the ion beam, the liquid-metal ion gunetc. can be used instead of the electron gun.

As mentioned above, the process quality of each process can be raised byattaining real-time measurement, becoming possible to measure theelectrostatic latent image of the photoconductor which the amount ofsurface electric charges decreases with time to the high resolution ofthe micron order, and feeding back the electrostatic latent image of themeasured photoconductor to the design by having the charging unitrequired in order to form the electrostatic latent image, and theexposure unit.

Accordingly, high resolution, the raise in the durability, highstabilization, and energy saving can be attained.

The scanning mechanism can be attached to the optical system of thecharged particle irradiation unit (electron beam irradiation unit) inthe present embodiment.

By adding the scanning mechanism, arbitrary latent-image patternsincluding the line pattern can be measured in the direction of the mainscanning of the cylindrical-form sample (photoconductor).

The example of composition of the exposure optical system which preparedthe scanning mechanism in the optical system of the charged particleirradiation unit (electron beam irradiation unit) in the presentembodiment is shown in FIG. 25.

The optical system of FIG. 25 comprises the light source 151 whichincludes the semiconductor laser (LD) of the wavelength which issensitive to the photoconductor 150 in the cylindrical form, thecollimator lens 152, the cylinder lens 153, the reflector mirror 154,the polygon mirror 155 as a deflector, the scanning lens L1 (156), andthe scanning lens L2 (157), etc.

The light source 151 is controlled by LD control unit which is notillustrated, and can be irradiated now on the suitable conditions.Therefore, the arbitrary electrostatic latent images which include theline pattern to the direction of the main scanning line can be measuredas mentioned above.

As a light source, by using the semiconductor laser (LD), it can containefficiently and control of the exposure time can be made easy into thelimited installation space.

Next, a description will be given of the insulation resistancemeasurement device according to the invention with reference to FIG. 26Athrough FIG. 31.

The insulation resistance measurement device according to the inventionis provided to measure an insulation resistance of a sample such as aphotoconductor with high precision in the order of micrometers.

FIG. 26A shows the composition of the insulation resistance measurementdevice in the preferred embodiment of the invention, which measures thedielectric intensity of a dielectric-substance sample 0.

In the composition of FIG. 26A, the dielectric-substance sample 0 havinga dielectric intensity being measured is placed on the conductiveplate-like support unit 223 which is grounded. In the upper part by theside of the surface of the dielectric-substance sample 0, the electronbeam irradiation unit 211A is arranged.

The electron beam irradiation unit 211A comprises the electron gun 210which emits the electron beam, the beam monitor 213, the condenser lens215, the aperture 217, the beam blanker 218, the scanning lens 219, andthe objective lens 221. These elements are connected to the power supplywhich is not illustrated and are controlled by the control unit (notshown) such as the computer.

The beam monitor 213 is provided for monitoring of the intensity of theelectron beam emitted by the electron gun 210, and the condenser lens215 is provided as the electron lens for converging the electron beamfrom the electron gun 210. The aperture 217 is provided for controllingthe current density (the quantity of irradiation potential per unittime) of the irradiation current by the electron beam, and the beamblanker 218 is provided for switching ON/OFF of the irradiation of theelectron beam to the dielectric-substance sample 0.

The scanning lens 219 is provided as the deflecting coil for making theelectron beam which passed the beam blanker 218 scan in atwo-dimensional manner, and the objective lens 221 is provided forconverging the scanning electron beam onto the surface of thedielectric-substance sample 0.

That is, the electron beam emitted from the electron gun 210 passes thebeam monitor 213, and is converged at the position of the aperture 217and the beam blanker 218 with the condenser lens 215, and deflected intwo-dimensional manner with the scanning lens 219 as the deflectingcoil. Thus, the deflected electron beam is converged toward the surfaceof the dielectric-substance sample 0 with the objective lens 221.

The electron beam which is deflected in two-dimensional manner with thescanning lens 219 scans the surface of the dielectric-substance sample 0in two-dimensional manner as mentioned above. That is, electron beamirradiation unit 211A and the control unit constitute the scanning unit.

In FIG. 26A, the reference numeral 225 denotes the charged particlecapture unit. The signal outputted from the charged particle captureunit 225 is sent to the signal processing unit which is not illustrated.For example, the signal processing unit may be provided as a part offunction of the computer which constitutes the control unit. Accordingto the information inputted, the signal processing unit performs thepredetermined processing and evaluates the dielectric intensity of thedielectric-substance sample 0.

That is, the charged particle capture unit 225 constitutes thesignal-detection unit. Moreover, the signal processing unit which is notillustrated may constitute the evaluation unit.

The electron beam irradiation unit 211A, the plate-like support unit223, and the charged particle capture unit 225 are accommodated in thesealed casing 230A, and the inside of the sealed casing 230A may bedecompressed to the substantial vacuum state by the suction unit 232.The suction unit 232 is controlled by the above-mentioned control unitwhich is not illustrated.

Therefore, the plate-like support unit 223, the sealed casing 230A, thesuction unit 232, and the control unit constitute a support unit whichholds the sample whose dielectric intensity is to be measured.

In the present embodiment, the scanning unit may be provided also as thecharging unit.

An example of the measurement by the insulation resistance measurementdevice of FIG. 26A which evaluates the dielectric intensity of thesample 0 when the dielectric-substance sample 0 is a thin-platepolycarbonate (PC) will be explained.

If the dielectric intensity of PC is the case where the thickness of thedielectric-substance sample is 50 micrometers when this is made intothis evaluation value since it is about 20 V/micrometer, it should justgive 1 kV or the charging potential beyond it in the thicknessdirection.

First, the dielectric-substance sample 0 is charged in the scan of theelectron beam. That is, the dielectric-substance sample 0 is charged asan charging unit using the scanning unit.

Electrification is performed so that the surface side of thedielectric-substance sample 0 may become negative polarity.

In the case where using the scanning unit, making it into the chargingunit is carried out the irradiation current at the time of charging theirradiation current at the time of the signal detection large carryingout and shortening charging time leads to shortening of the measuringtime. In order to change the amount of irradiation current (currentdensity) electrically, it is good to change the amount of current whichchanges the focal length of the condenser lens 215 electrically, andpasses the aperture 217.

That is, the irradiation current which a part of electron beam isintercepted by the aperture 217 since incidence is carried out to theaperture 217, the electron beam converging before the aperture 217 andemitting if the focal length of the condenser lens 215 is shortened asit is shown in FIG. 26C, although irradiation current is large if theelectron beam is converged on the opening of the aperture 217 with thecondenser lens 215 as shown in FIG. 26B, and goes to thedielectric-substance sample 0 becomes small.

Even if it makes the focal length of the condenser lens 215 longer thanthe case of FIG. 26B, irradiation current can be made small as mentionedabove.

It is possible also by changing the diameter of the aperture 217 tochange the size of irradiation current. In addition, by adjustment withthe aperture 217 and the condenser lens 215, irradiation current can bechanged or can be changed.

Although the condenser lens 215 is the electromagnetic lens in theexample under explanation, the same is said of the electrostatic lens.

When charging the dielectric-substance sample 0, the irradiation currentis made larger than the time of the signal detection, and themeasurement region (for example, 1 mm around) of the surface of thedielectric-substance sample 0 is scanned in two-dimensional manner.

At this time, the charging polarity of the dielectric-substance sample 0changes with the magnitude of acceleration voltage E of the electronbeam. Namely, the secondary-electron-emission ratio (delta) isrepresented by the formula delta=Not/Nin, where Not is the secondaryelectron number discharged and Nin is the incidence electron numberirradiated.

If the acceleration voltage is gradually increased from 0 and energy ofthe electron beam is enlarged, the secondary electron number emittedwill increase initially, but, with increase of the acceleration voltage,the secondary electron number reaches the maximum and it will decreaseafter the maximum is reached.

That is, the secondary-electron-emission ratio delta increases initiallywith increase of the acceleration voltage, and it is set to delta=1 bythe acceleration voltage E1, and if the acceleration voltage increasesafter that, after greeting the maximum, it decreases to one or less morethan by acceleration voltage E2.

Therefore, if acceleration voltage E is set as the range of E1<=E<=E2,the surface of the dielectric-substance sample 0 will be charged inpositive polarity with the scan of the electron beam.

The acceleration voltage set to one in the example under explanationafter secondary-electron-emission ratio delta exceeds the maximum. It isset as acceleration voltage (E>E2) higher than E2, and negative chargingof the dielectric-substance sample 0 is carried out. Thus, if thetwo-dimensional scan is performed, in order that the amount of incidenceelectrons by the scan may exceed the amount of discharge electrons, theelectron will be accumulated at the surface of the dielectric-substancesample 0, and uniform charging of the surface side of thedielectric-substance sample 0 will be carried out at negative polarity.In FIG. 26A, the letter C denotes the accumulated electron.

Moreover, since the plate-like support unit 223 close to the backsurface of the dielectric-substance sample 0 is grounded by theconductivity, the positive charge (indicated by the letter D in FIG.26A) which balances with the minus electric charge by the side of thesurface of the dielectric-substance sample 0 will be excited on theborder plane with the dielectric-substance sample 0, and field intensitywill be given in the thickness direction of the dielectric-substancesample 0.

The acceleration voltage the desired charging potential can be formed bysetting up E and irradiation time appropriately.

If charging is continued after the dielectric-substance sample 0 reachesthe charging potential of 1 kV, charging voltage increases, andpartially, by the bad part of the dielectric intensity, the breakdownwill arise, the hole will flow into the dielectric-substance sample 0from the plate-like support unit 223, and it will offset the minuselectric charge by the side of the sample surface.

Such electric offset arises locally and the electric charge distributionarises in the surface side of the dielectric-substance sample 0. And theelectric field distribution according to the surface electric chargedistribution is formed in the space by the side of the surface of thedielectric-substance sample 0.

In this state, the amount of current of the irradiation current by thescanning unit is changed to the signal detections, and thetwo-dimensional scan for the signal detections is performed.

And the secondary electron “es” is captured with the charged particlecapture unit 225. The charged particle capture unit 225 is what combinedthe scintillator (phosphor) and the photoelectron redoubling pipe, andthe secondary electron es applied and drawn to the surface of thescintillator by power supply (not shown), is captured by thescintillator by the electric field of voltage, and is changed intoscintillation light. Through the light pipe, with the photo multipliertube, this light is amplified as the current and taken out as adetection signal (current signal).

FIG. 27A shows the potential distribution in the space between thescintillator 224 and the dielectric-substance sample 0 in the chargedparticle capture unit 225 wherein the distribution is indicated by thecontour line display. The surface of the dielectric-substance sample 0is in the state uniformly charged in negative polarity, if the portionwhich potential decreased by the breakdown is removed, and it becomes asit approaches the scintillator 224 from the surface of thedielectric-substance sample 0 in the potential contour line group shownas the solid line, since the potential of positive polarity is given tothe scintillator 224 of the charged particle capture unit 225.

Therefore, the secondary electrons el1 and el2 generated in Q1 point ofFIG. 27A, which is the portion which carries out uniform charging atnegative polarity in the dielectric-substance sample 0, or Q2 point arepulled to the right potential of the charged particle capture unit 224,as shown in the arrow G1 or G2, they are displaced, and they arecaptured by the scintillator 224.

The portion into which the negative potential decreased Q3 point bybreakdown in FIG. 28A on the other hand it is about Q3 point thearrangement of the potential contour line, so that it is as the dashedline shows, and it is close to Q3 point in this partial potentialdistribution potential becomes high. If it puts in another way, as thearrow G3 shows, the electric force restrained to thedielectric-substance sample 0 side will act on the secondary electronel3 generated in Q3 point near.

For this reason, the secondary electron el3 is captured in the potentialhole which the potential contour line of the dashed line shows, and doesnot move toward the charged particle capture unit 224. FIG. 28B showsthe potential hole typically.

The intensity (secondary electron number) of the secondary electrondetected with the charged particle capture unit 225 includes the portionwith large intensity the normal portion by which the breakdown is notcarried out (it is the portion which carries out negative charginguniformly). It will correspond to the portion represented by the pointQ1 or Q2 of FIG. 28A, and the portion with small intensity will beequivalent to the portion (which is represented by the point Q3 of FIG.28A) into which the negative potential decreased as an absolute value bythe breakdown.

At this time, 2-dimensional coordinates express region (evaluationregion) S scanned by the electron beam in two-dimensional manner by S (xy). For example, the region is 0 mm≦x≦1 mm. 0 mm≦y≦1 mm.

This region where the surface potential distribution currently formed inS (x y) is set to V (x y) (<0). If the time to result from the start ofthe two-dimensional scan of the dielectric-substance sample 0 by theelectron beam in the end is made into T0<=T<=TF, the time T when thescan is performed corresponds to each scanning position in scanningregion S (x y), and there is the one-to-one correspondence.

Therefore, the electric signal (detection signal) acquired by thesecondary electronic detecting element 225 is sampled by the suitablesampling time, and, with the signal processing unit, the surfacepotential distribution V (X, Y) can be determined for every minuteregion corresponding to the sampling time by making the sampling instant(tau) into the parameter. In the signal processing unit, the surfacepotential distribution V (X, Y) is constituted as the two-dimensionalimage data, and it is outputted to the output device (not shown). Theoutput device is formed as a part of the evaluation unit is made. Thus,the state of the breakdown in the evaluation region will be obtained byusing the output device as a visible image.

For example, if the intensity of the secondary electron captured isrepresented by the intensity of brightness of the image, the imageportion of the normal portion where negative charging is made uniformlybecomes bright, and the portion (the portion of potential damping) wherethe breakdown arises becomes dark, and it can be outputted as alight-and-dark image.

In addition, even if the actual evaluation region is minute, the imageoutputted from the output device is suitably expandable to the size ofthe request suitable for observation.

Thus, it can determine whether the dielectric-substance sample 0 startsthe breakdown or where the breakdown occurs, as a result the insulationresistance can be evaluated.

The insulation resistance measurement device described above with FIG.26A comprises the support unit 223 and 230A which holds the sample 0whose dielectric intensity is to be measured, the charging unit 211Awhich charges the sample 0 held by the support unit and gives electricfield intensity in the thickness direction of the sample, the scanningunit 21 IA which scans the surface of the charged sample 0 with thecharged particle beam, the signal-detection unit 225 which obtains thedetection signal by the scanning of the scanning unit, and theevaluation unit (signal processing unit which is not illustrated) whichevaluates the dielectric intensity of the sample 0 based on the signaldetected by the signal-detection unit.

Moreover, in the above-described insulation resistance measurementdevice, the electric field intensity of 10 V/micrometer or more is givenin the thickness direction of the sample 0, the electron beam is used asthe charged particle beam which scans the surface of the sample 0, andthe scanning unit 211A which irradiates the electron beam is used as thecharging unit which charges the sample 0.

Moreover, in the above-described insulation resistance measurementdevice, the scanning unit which irradiates the electron beam comprisesthe condenser lens 215 and the aperture 217, and selectively changes theamount of irradiation current between the time of acquiring thedetection signal and the time of charging the sample 0 by using thecondenser lens 215 and/or the aperture 217. And the secondary electronof the electron beam is detected and the detection signal is acquired.

Moreover, in the above-described embodiment, the electric charge leaklocation (the portion where potential damping arises due to electriccharge leaking caused by the breakdown) in the sample is detected basedon the detection signal which is obtained by detecting the secondaryelectron.

According to the insulation resistance measurement device of FIG. 26A,the surface of the sample 0 which is charged and gave the electric fieldintensity in the thickness direction is scanned in two-dimensionalmanner with the charged particle beam, and the insulation resistancemeasurement in which the dielectric intensity of the sample 0 isevaluated is carried out based on the detection signal acquired by thescanning.

Moreover, in the insulation resistance measurement device of FIG. 26A,the latent-image support object may be used as the sample whosedielectric intensity is to be measured. Hereafter, a description will begiven of such insulation resistance measurement device.

In the following embodiment, as a latent-image support object, thephotoconductor of function separation type mentioned above is taken foran example.

FIG. 28A shows the structure of the photoconductor 01 of functionseparation type.

As is well known, the photoconductor 01 is formed in the composition sothat the lower coat layer 310 is formed on the conductive substrate 300,and the laminating of the electric charge generation layer 320 and theelectric charge transportation layer 330 is performed on the lower coatlayer 310.

In FIG. 28A, there is shown the photoconductor (which is a latent-imagesupport object) as the dielectric-substance sample 01. In the state ofFIG. 28A, the sample 01 is placed on the plate-like support unit 223 ofFIG. 26A, and negative charging of the surface layer is performed withthe electrons C by the scanning of the electron beam similar to theprevious embodiment.

At this time, the positive charge D is injected into the conductivesubstrate 300 from the plate-like support unit 223, and it is excited onthe boundary with the lower coat layer 310.

The upper figure of FIG. 28B shows typically the state where thebreakdown arose into the portion shown with the signs DM1 and DM2 of thephotoconductor 01. In these portions DM1 and DM2, the hole (electronhole) is poured into the lower coat layer 310 from the substrate 300side, the electric charge generation layer 320 and the electric chargetransportation layer 330 are moved, and the minus electric charge by theside of the photoconductor surface is canceled. The charged potential ofthe portion is damped by the cancellation.

The lower figure of FIG. 28B shows the state of this potential dampingtypically. If the visible conversion to signals of the state (electriccharge leak location) where scanned by the electron beam, captured thesecondary electron generated with the scan with the charged particlecapture unit 225, acquired the detection signal, and processed this inthe signal processing unit, for example, the breakdown is carried out iscarried out as such a state was explained previously, as shown in FIG.28C will be obtained.

Specifically, the absolute value EA of the field intensity acting in thethickness direction of the photoconductor is set to EA=|V/d|=30V/micrometer, where the film thickness of the photoconductor 300 (thetotal thickness of the lower coat layer 310, the electric-chargegeneration layer 320, and the electric-charge transportation layer 330)is d=30 micrometer, and the charging potential is V=−900V.

If the lower coat layer 310 does not withstand the electric fieldintensity EA, the electric charge leak occurs with hole blocking fromthe location of the lower coat layer 310 where the dielectric intensityis the weakest, and the hole arrives at even the photoconductor surface,which cancels the minus electric charge on the surface of thephotoconductor and causes the electric charge distribution to arise onthe surface. The secondary electron in this state is detected by thescanning of the electron beam, and it is possible to determine theelectric charge leak location (FIG. 28C) by the breakdown with highprecision in the order of micrometers.

It is desirable that the total amount of electric charges irradiated tothe sample per unit area is larger than 1E-8 coulomb/mm² in the casewhere the dielectric intensity is evaluated by making the latent-imagesupport object into the dielectric-substance sample. The total electriccharge per unit area (charge density) Cm is represented by the formulaCm=A t/S where A is the irradiation current A, S is the irradiationarea, and t is the irradiation time. For example, the appropriatecondition is the irradiation current 5E-10A, the irradiation area 1 mm²,and the irradiation time 20 seconds. It is appropriate that theirradiation time t is lengthened in proportion to the irradiation areaS. If the irradiation current A is enlarged, the irradiation time tbecomes shorter accordingly.

If the irradiation time is lengthened and the total amount of electriccharges irradiated to the sample is increased, the electric charge leaklocation will appear notably so much.

For example, if the irradiation is performed for 5 minutes in theconditions of the irradiation current 1E-9A and the irradiation area 1mm², the total amount of electric charges is set to 3E-7 coulomb/mm²,and time will be taken somewhat. However, the electric charge leaklocation appears notably, which clarifies the difference between aconforming product and a defective product.

Usually, the isolation resistance voltage required for the latent-imagesupport object is usually 30 V/micrometer or more, and for the higherend version is 40 V/micrometer. It is desirable that the percentage ofthe electric charge leak region (which is the ratio of the area s of theelectric charge leak region to the whole surface area SA of theevaluation region) is 1% or less under the conditions. It is known byexperience that it is not conspicuous as ground dirt in the output imageif the percentage of the electric charge leak region is 1% or less.

Therefore, the conditions for the latent-image support object being aconforming product are that the isolation resistance voltage is above 30V/micrometer and below 40 V/micrometer, the amount of electronirradiated to the sample is above 1 nano-coulomb/mm², and the percentageof the insulation resistance region (which the ratio of the area of theregion where the breakdown does not occur to the whole area of theevaluation region) is 99% or more.

FIG. 29A shows the result of measurement when the irradiation to thelatent-image support object is continued for the irradiation time t=4minutes by the irradiation current A=1E-9A and the irradiation areaS=1.47 mm².

The charge density Cm irradiated in this example is Cm=At/S=1.6E-7coulomb/mm². The insulation resistance is so high that the ratio of thearea of the region where the electric charge leak occurs is small atthis time.

In the example of FIG. 29A, the electric charge leak area ratio 1.2%,and the insulation resistance region ratio is 98.8%, and it is foundthat this sample is a defective product in which ground dirt tends toappear. On the other hand, in the example of FIG. 29B, the electriccharge leak area ratio is 0.4%, and it is found that this sample is aconforming product in which the hole size is sufficiently small.

In the case of the latent-image support object, as far as electriccharge leak is concerned, the photoconductor sample with the insulationresistance high and there are few leak regions is better. However, ifthe insulation resistance is high too much, there is a possibility thatthe potential does not fully fall when it is made to exposure may arise.By taking into consideration this matter, it can be said that thephotoconductor with the electric charge leak region percentage in therange of between 0.05% and 1.0% is a conforming product.

FIG. 30 shows another embodiment of the insulation resistancemeasurement device.

In FIG. 30, the elements which are the same as corresponding elements inFIG. 26A are designated by the same reference numerals, and adescription thereof will be omitted for the sake of convenience ofexplanation.

In the embodiment of FIG. 30, the dielectric-substance sample 01 is thelatent-image support object, and is the photoconductor of functionseparation type mentioned above with FIG. 28A.

The dielectric-substance sample 01 is formed in the shape of aphotoconductor drum, and uniform rotation is carried out in thedirection of the arrow (counterclockwise rotation) by the drive unitwhich is not illustrated. After the sample 01 is set in the casing 230A,the inside of casing 230A is highly decompressed by the suction unit232.

The charging unit 242 is, for example, a contact type charging unithaving the charging brush, the charging roller, etc., and carries outcontact charging of the dielectric-substance sample 01 uniformly withinthe casing under pressure reduction.

At this time, uniform rotation of the sample 01 is carried out in thedirection of the arrow (counterclockwise rotation).

Of course, the dielectric-substance sample 01 can also be charged bycharging using the electron beam as in the example of FIG. 26A.

Although the scan of the electron beam by electron beam irradiation unit211A may be performed by deflecting the electron beam in two-dimensionalmanner as in the embodiment of FIG. 26A, since the scan is received thedielectric-substance sample 01 carrying out uniform rotation in thedirection of the arrow, the electron beam can be deflected in onedimension in the direction which intersects perpendicularly with thedrawing, and the two-dimensional scanning can also be realized combiningthis deviation and rotation of the dielectric-substance sample 01.

The electric discharge lamp 229A, preceding measuring the dielectricintensity, irradiates uniformly the surface of the dielectric-substancesample 01 which is uniformly rotated, and makes the state of thedielectric-substance sample 01 suitable for measurement.

In addition, what is necessary is to be able to use other chargedparticle beam, for example, the ion beam, and just to, use theliquid-metal ion gun etc. instead of the electron gun in that case, ofcourse, although each form of the operation explained above explainedthe case where the electron beam was used as a charged particle beam.

FIG. 31 is a flowchart for explaining the procedure of insulationresistance measurement the measurement in the preferred embodiment ofthe invention.

As shown in FIG. 31, the dielectric-substance sample (for example, thelatent-image support object) is set in the measurement device (it isheld by the support unit) (S201), and it is charged by the electron beamirradiation (S202).

Subsequently, the secondary electron which performs electronic linescanning and is generated by the dielectric-substance sample is detected(S203), and the 2-dimensional image is mapped based on the detectionresult (S204).

Subsequently, the data in each pixel of the mapped 2-dimensional imageis converted into the binary value with a predetermined threshold level(S205). In this state, as shown in FIG. 29A or FIG. 29B, the monochromeimage is obtained.

Then, the electric-charge leak location is determined (S206), and thegross area (computed as the sum of the number of the black pixels) ofthe electric-charge leak location (black portion) (S207). Then, the areapercentage to the evaluation region is computed, and it is determinedwhether the latent-image support object is a conforming product based onthe result of computation.

Next, FIG. 32 shows the composition of the electrostatic latent imagemeasurement in the preferred embodiment of the invention.

In FIG. 32, the reference numeral 301 denotes the electron gun, 302denotes the condenser lens, 303 denotes the beam blanker, 304 denotesthe scanning lens, 305 denotes the objective lens, 306 denotes thesample, such as a photoconductor, 307 denotes the conductor, 100 denotesthe charged particle irradiation unit, 200 denotes the sampleinstallation unit, 306, and B denotes the electron beam or the ion beam,respectively.

The measurement device in this embodiment comprises the charged particleirradiation unit 100 which irradiates the charged particle beam, and thesample installation unit 200.

The charged particle in this embodiment is the particle which isinfluenced in the electric field, such as the electron beam or the ionbeam, or the magnetic field.

In the following, the embodiment which irradiates the electron beam willbe explained.

The electron beam irradiation unit 100 comprises the electron opticalsystem, such as the beam blanker (not shown) for making ON/OFF thecondenser lens 302 and electron beam for converging the electron beamgenerated from the electron gun 301 for generating the electron beam,and the electron gun 301, and the objective lens 305 for making thescanning lens 304 and scanning lens for making the inside of thecharging region scan by the electron beam condense again. The powersupply for the drive which is not illustrated is connected to each lens.

In addition, when the beam diameter is equivalent to the chargingregion, there may not be the scanning lens 304. It has the field whichcharges the sample, and composition which can impress potential Vg tothe sample back surface.

The electron optics system and the sample unit are arranged in thevacuum so that the orbit where the electron is exact may be progressed.

The electron beam B is generated to irradiate the photoconductor sample306. By setting the acceleration voltage E1 (>0) higher than theacceleration voltage E0 (>0) at which the secondary-electron-emissionratio delta is set to 1, so that the amount of incidence electronsexceeds the amount of discharge electrons, the electrons are accumulatedin the sample and the charge increasing starts. Consequently, the sample306 is charged in negative polarity. The desired charging potential canbe formed by setting the acceleration voltage and the irradiation timeappropriately.

In the present embodiment, the secondary-electron-emission ratio (delta)is represented by the formula delta=discharge electron/incidenceelectron. More strictly speaking, it is necessary to take intoconsideration the penetration electron and the reflection electron, and,in such a case, it is appropriate to consider the discharge electron inthe above formula as the discharge electron=penetrationelectronic+reflection electron+secondary electron.

In this respect, E0 is an acceleration voltage of electrons at which thesecondary-electron-emission ratio of the sample is equal to 1 when theback surface of the sample is grounded (GND). E0 is equivalent tocharging starting potential.

FIG. 33 shows the relation between acceleration voltage and charging.FIG. 34 shows the relation between the irradiation time of the electronbeam and the charging potential. FIG. 35 shows the relation betweenacceleration voltage and charging potential.

Generally the secondary-electron-emission ratio delta is the relationlike FIG. 33 depending on the energy of the electron beam, i.e.,acceleration voltage.

In the acceleration voltage E1 (>0) used as delta=1, charging does notoccur but equilibrium is maintained. In the case of the accelerationvoltage E1>E0, it is set to delta<1, and there are few dischargeelectrons compared with the incidence electron number, it becomesnegative charging.

The relation between acceleration voltage and irradiation time is shownin FIG. 34.

Although the electric charge is rapidly accumulated immediately afterelectron beam irradiation, according to progress of time, the incidenceelectron is slowed down under the influence of the negative chargingpotential of the sample. If the mass of electrons is set to m and theamount of electric charge is set to e, the speed (landing speed) v atthe time of the electron surface attainment in the surface potentialvoltage Vp (>0) is represented by the formula v={2e(E1+Vp)}^(1/2) inapproximation (1).

Therefore, with the electric charge accumulation (negative charging),the landing speed decreases, and the amount of electric chargeaccumulation per unit time decreases, namely: E1+Vp=E0. If it becomesthe condition of Vp=E0−E1 (2), the balanced stable state will be reachedand the state Vd, i.e., the saturation charging potential, where it isnot charged any more will be reached.

FIG. 35 shows an example of the relation of the saturation chargingpotential of the acceleration voltage.

The surface potential voltage Vp is represented by the sum of thepotential Vs of the sample electric charge accumulation side accordingto the sample surface charge density Qs and the potential Vg of thesample back surface, namely: Vp=Vs+Vg (3) whereVs=Q/C=d/(S×epsilon′×epsilon0)×Qs, epsilon′ is the specific inductivecapacity, epsilon0 is the dielectric constant of vacuum, Q is the amountof electric charge accumulation, S is the unit area, and d is thethickness of the sample. In this case, the characteristic values of thesample are fixed, and the relation of Vs□Qs is materialized.

FIG. 36 shows the measurement result of the present embodiment. It ispossible to control the potential Vs produced by the sample surfacedensity of charge Qs by controlling the voltage Vg applied to the sampleback surface, etc.

The measurement result of FIG. 36 is the result of measurement of thesaturation charging potential when the acceleration voltage is fixed at1.5 kV and the potential Vg of the back surface of the sample is varied.It is made into Vg=0V at the time of the measurement result. Thepolarity of the voltage is (−V).

At the time of Vg=0V, the potential is −550V. As a result of this,E0=−950V in this sample. If Vg is changed to the plus side, theincidence electron will be accelerated relatively, it will become easyto be charged, the amount of electric charge accumulation will increase,and charging potential will rise in the minus direction.

Moreover, if Vg is changed to the minus side, the incidence electronwill be slowed down relatively, it will be hard coming to be charged,the amount of electric charge accumulation will decrease, and chargingpotential will fall.

Moreover, the following relation is materialized in the relation betweencharging potential and applied voltage by approximation: Saturationcharging potential Vd (−V)=acceleration voltage E1(V)−charging startingpotential E0 (V)+applied voltage Vg (V) (4).

Therefore, if Vg=0 and the acceleration voltage of 1.5 kV, the samplecan be charged only to −550V at the maximum. By applying the voltage ofVg=300V, the same sample can be charged to −850V. By applying a highervoltage for Vg, a higher charging potential can be obtained.

Since the amount of electric charge accumulation changes with time likeFIG. 34, it is controlling Vg and charging time. It is possible toobtain the charging potential Vs which fulfills the conditions of|E1−E0+Vg|>=|Vs|. Since the acceleration voltage can stop low comparedwith the former the feature that there is little power dissipation andit is suitable for the environment and the control is also easy toperform.

It becomes impossible it not only to become difficult to control, sincetime to reach target charging potential will become short ifacceleration voltage becomes large, but to disregard the damage to thesample. Therefore, the conditions which can form desired chargingpotential are desirable at as small acceleration voltage as possible.

|Vs|<=|E1−E0+Vg|<=|Vs|+2 kV(5) is suitable.

Although about E1=1.75-3.75 kV is the proper range in the case of Vg=0in order to charge Vs=−800V by this sample (E0=−950V), it is realizableby E1=1−3 kV and low acceleration voltage by setting up with Vg=750V.

In addition, what is necessary is just to increase the current densityof the electron beam, in order to make it charged in short time.

Although the charging unit by lower voltage impression is applicablewith the charging-among the atmosphere method, if it is in the vacuum,since the charged particle will not receive interference by the particlein the atmosphere, it can perform high charging formation of accuracy.

FIG. 37 is a diagram for explaining the example of latent-imageformation and measurement. FIG. 38 is a diagram showing an example ofthe exposure optical system.

In FIG. 37, the reference numeral 310 denotes the light source, 311denotes the collimator lens, 312 denotes the aperture, 313 denotes thescanning lens, 315 denotes the LD control unit, 316 denotes the electriccharge detector, and 300 shows the exposure optical system,respectively.

In FIG. 38, the reference numeral 320 denotes the light source, 321denotes the collimator lens, 323 denotes the cylinder lens, 324 denotesthe scanning lens, 326 denotes the 1st reflector mirror, 327 denotes thepolygon mirror, 328 denotes the 2nd reflector mirror, and 329 denotesthe photoconductor drum, respectively.

The latent-image formation unit will now be explained. It is exposed bythe exposure optical system 300 after charging of the predeterminedquantity in the photoconductor sample 306 at the photoconductor sample306.

The exposure optical system 300 is adjusted so that the desired beamdiameter and the desired beam profile may be formed.

It comprises the light sources 310, such as LD (laser diode) which hasthe wavelength of the sensitivity region of the photoconductor sample306, the collimator lens 311, aperture 312, the cylinder lens 313, thescanning lens 14, etc., and the desired beam diameter and the beamprofile are created on the sample 306.

The suitable exposure time and exposure energy can be irradiated now bythe LD control unit 315.

As shown in FIG. 38, arbitrary latent-image patterns including the linepattern can be formed to the direction of the main scanning of thephotoconductor drum 329 by attaching the scanning mechanism using thepolygon mirror 327. Thereby, the electrostatic latent image can beformed in the photoconductor sample.

The conditions are changed into the electrostatic latent image of thephotoconductor sample, it scans by the electron beam, and the secondaryelectron emitted is detected by the electric charge detector(scintillator) 316, it changes into the electric signal, and thepotential contrast image is measured.

If the electric charge distribution is shown in the sample surface, theelectric field distribution according to the electric chargedistribution will be formed in space. For this reason, the secondaryelectron generated by the incidence electron is put back by thiselectric field, and the quantity which reaches the detector 316decreases.

Therefore, the portion with strong field strength is dark, contrast canattach the weak portion brightly and the contrast image according to thesurface electric charge distribution can be detected. When it exposes,black and the non-exposing unit serve as the exposure unit white.

Therefore, when the electron beam scans the sample side and carries outthe signal detection by it, the formed electrostatic latent image can bemeasured. When changing with setting conditions, you may rectify thesignal strength on the detector.

Moreover, it is possible to carry out the calibration in advance.Moreover, it is possible to detect the reflection electron instead ofthe secondary electron. After the measurement end can remove theresidual charge by using LED etc. and irradiating the whole sample side.

The composition of the control unit of the present invention is shown inFIG. 37.

FIG. 39 is a diagram for explaining the embodiment which measures theelectrostatic latent image of the photoconductor of cylinder form.

In the chamber, the electric discharge unit 332 for eliminating theexposure unit 331 for making the charging unit 330 for making theelectric charge irradiate and the electric charge distribution formaround the photoconductor sample 329 of cylinder form and thephotoconductor sample and the electric charge is. The drive unit whichcan be rotated is attached in the photoconductor 329 to thephotoconductor center axis.

There are the stepping motor, the DC-servo motor, etc. as the driveunit. As the charging unit 330, there are charging by electron beamirradiation, electric charge pouring charging, such as contact charging,etc. There is the LED etc. as the electric discharge unit. The operationof this embodiment will be described.

In the charging unit, it has the inner side of the photoconductor, i.e.,the charging surface, and composition which can impress the voltage Vgof the opposite side, and the photoconductor is uniformly electrified sothat the photoconductor surface may serve as desired potential, wherethe seal of approval of the voltage of Vg is carried out.

The applied voltage of the photoconductor lower electrode is set as thegrounding state (GND).

In the exposure unit, light is irradiated to the photoconductor, theelectric charge is missed partially, and the electrostatic latent imageis formed.

In the measurement unit, the photoconductor sample is scanned by theelectron beam, the electron emitted is detected by the scintillator, itchanges into the electric signal, and the potential contrast image isobserved.

In the electric discharge unit, the residual charge on thephotoconductor is erased by irradiating LED etc. By using such a method,even if it is cylinder form, it is possible to measure the electrostaticlatent image of the photoconductor. In addition, although the appliedvoltage of the photoconductor lower electrode was set as the groundingstate (GND), voltage may be impressed depending on the image formationunit.

FIG. 40 is a diagram showing the composition of another embodiment.

In FIG. 40, the letter P denotes the opposite electrode. Thephotoconductor drum 329 which is the dielectric-substance unit rotates,and since the electric conduction unit to impress is fixed, it canimpress the independent voltage by preparing opposite voltage for everyimpression process. The opposite electrode P is made fixationcorresponding to the peripheral device of the photoconductor.

FIG. 41 is a diagram showing the composition of another embodiment.

In FIG. 41, the letter p denotes the conductor with the opposingelectrodes. The inside conductor the portion p and the conductor bypreparing the crevice between the insulated units between the portionsp, it makes it possible to impress the voltage of the request whichbecame independent in each process in this case, the conductor it may bemade to correspond to the peripheral device, you may fix, and theportion p may make it rotate united with the photoconductor.

FIG. 42 shows another embodiment. FIG. 43 is a diagram for explainingthe charging unit which is the corotron changing device.

The photoconductor peripheral device is used for the image formingapparatus. It is charged in the atmosphere, the differential exhaust isused, and the latent image is measured in the vacuum state.

The corona discharging can be used as the charging unit in theatmosphere as shown in FIG. 43, and the corotron charging device or thelike can be used, and the same effect as described above can be acquiredby supplying the applied voltage to the lower part of the sample. Inthis case, a small amount of the ozone occurs and it is suitable for theenvironment.

In addition, it is possible to apply this charging device to the imageforming apparatus.

As long as there is the sample by the dielectric substance, latent-imageformation units may be the methods which form the electric chargedistribution directly, such as the electrostatic recording method. Whenthe sample is the photoconductor, the latent-image formation unit whichincludes the charging unit and the exposure unit may be used for themethod.

Moreover, when the sample measures the photoconductor of cylinder form,it can take the composition shown in FIG. 42. By using such a method, itbecomes possible to measure the electrostatic latent image of thephotoconductor in the state near real use environment.

Moreover, it becomes possible to measure the distribution state of theelectrostatic latent image for hundreds of or less ms equivalent toprocess speed.

The present invention is not limited to the above-described embodiments,and variations and modifications may be made without departing from thescope of the present invention.

1. A charging device which creates electric charge on abeam-irradiation-side surface of a sample by irradiating a negativecharged particle beam, including electrons or negative charged ions, tothe sample, wherein the charging device is provided to meet theconditions E1>E0−Vg, E0>0, and E1>0 where E0 is an acceleration voltageof electrons at which a secondary-electron-emission ratio of the same isequal to 1 when a back surface of the sample opposite to thebeam-irradiation-side surface is grounded, E1 is an acceleration voltagefor accelerating negative charged particles of the beam, and Vg is aback potential applied to the back surface, so that a desired negativecharging potential is formed on the sample.
 2. The charging deviceaccording to claim 1, wherein the back potential Vg applied to the backsurface meets the conditions |E1−E0+Vg|≧|Vs| where Vs is the desirednegative charging potential.
 3. The charging device according to claim2, wherein the back potential Vg applied to the back surface furthermeets the conditions |E1−E0+Vg|≦|Vs|+2 kV.
 4. The charging deviceaccording to claim 1, wherein the charging device is provided to createthe electric charge on the sample in a vacuum state.
 5. The chargingdevice according to claim 1, wherein the back potential Vg is set tozero and the back surface is grounded after the electric charge iscreated on the sample.
 6. The charging device according to claim 1,wherein the charging device comprises a unit which sets the backpotential Vg to a spatially different value for another sample.
 7. Anelectrostatic latent-image measurement device comprising: a chargingdevice creating electric charge on a beam-irradiation-side surface of asample by irradiating a negative charged particle beam, includingelectrons or negative charged ions, to the sample; and an exposureoptical system irradiating light to the charged surface of the sample sothat an electrostatic latent image according to an electric chargedistribution of the sample surface is formed, wherein the chargingdevice is provided to meet the conditions E1>E0−Vg, E0>0 and E1>0 whereE0 is an acceleration voltage of electrons at which asecondary-electron-emission ratio of the same is equal to 1 when a backsurface of the sample opposite to the beam-irradiation-side surface isgrounded, E1 is an acceleration voltage for accelerating negativecharged particles of the beam, and Vg is a back potential applied to theback surface, so that a desired negative charging potential is formed onthe sample.
 8. The electrostatic latent-image measurement deviceaccording to claim 7, wherein the charging device is provided to createthe electric charge on the sample in a vacuum state.
 9. Theelectrostatic latent-image measurement device according to claim 7,wherein a measurement unit is provided to measure the electrostaticlatent image of the sample surface by scanning the sample surface by anelectron beam.
 10. The electrostatic latent-image measurement deviceaccording to claim 9, wherein the measurement unit is provided to detecta secondary discharge electron from the sample.
 11. An electrostaticlatent-image measuring method for an electrostatic latent-imagemeasurement device, comprising: creating, by a charging device, electriccharge on a beam-irradiation-side surface of a sample by irradiating anegative charged particle beam, including electrons or negative chargedions, to the sample; and irradiating, by an exposure optical system,light to the charged surface of the sample so that an electrostaticlatent image according to an electric charge distribution of the samplesurface is formed, wherein the creating of the electric charge meets theconditions E1>E0−Vg, E0>0 and E1>0 where E0 is an acceleration voltageof electrons at which a secondary-electron-emission ratio of the same isequal to 1 when a back surface of the sample opposite to thebeam-irradiation-side surface is grounded, E1 is an acceleration voltagefor accelerating negative charged particles of the beam, and Vg is aback potential applied to the back surface, so that a desired negativecharging potential is formed on the sample.